Optical recording/reproducing apparatus

ABSTRACT

In an optical recording/reproducing apparatus of the present invention, a semiconductor laser driver supplies a selected one of a plurality of drive currents, including at least a first-level drive current and a second-level drive current, to a semiconductor laser to control the emission of a laser beam by the laser. A current driver selectively outputs one of a plurality of increment currents to the laser driver in response to control signals, the plurality of increment currents including a first increment current supplied to the laser driver during an automatic power control process and a second increment current supplied to the laser driver during a special power setting process. A detection unit detects a first power sample signal, at a first sampling point of a laser driving current waveform, from the laser beam emitted when the first increment current is supplied to the laser driver, and detects a second power sample signal, at a second sampling point of the waveform, from the laser beam emitted when the second increment current is supplied to the laser driver. A calculation unit calculates a derivative efficiency of the laser based on the first and second power sample signals detected by the detection unit, so that the drive currents of the laser driver, supplied to the laser, are controlled based on the calculated derivative efficiency.

BACKGROUND OF THE INVENTION

[0001] 1. Field of The Invention

[0002] The present invention relates to an optical recording/reproducingapparatus which records information onto or reproduces information froma recording medium, such as an optical disk, by focusing a laser beamemitted by a semiconductor laser, on a recording layer of the recordingmedium.

[0003] 2. Description of The Related Art

[0004] In these years, there are various optical read-only recordingmedia, such as CD (compact disk), CD-ROM (compact disk read-onlymemory), DVD (digital versatile disk), etc., and optical reproducingsystems, or optical disk players, which reproduce information from theserecording media, are put into practical use.

[0005] In addition, the read-only recording media have their rewritableequivalents, including optical write-once read-many recording media(such as CD-R), magneto-optical recording media (such as MO), andphase-change recording media (such as DVD- rewritable). The specialattention is given to the phase-change recording media (typically,DVD-rewritable disks) as mass-storage recording media in the nextgeneration, and optical recording/reproducing systems, or optical diskdrives, which record data onto and reproduce data from the phase-changemedia are proceeding towards practical applications.

[0006] The phase-change recording media utilize a process called thephase change technology to write and erase data. In this process, datais written to the phase-change recording disk by focusing ahigh-intensity laser beam on a recording layer of a phase-changematerial embedded in the substrate of the disk. In its original state ofthe phase-change material, the recording layer has a crystallinestructure. The laser beam selectively heats areas of the surface portionof the disk to a high temperature. Where the beam strikes, the heatmelts the crystals to a non-crystalline, or amorphous phase. These areasreflect less light than the unchanged area surrounding them.

[0007] When a weaker laser beam, used to read data from the disk,strikes the amorphous area, the beam is scattered and not picked up bythe light-sensitive diode in the read head of the disk drive. With thelower reflectance, these areas become marks, representing “1”s. Areasthat are not heated are more reflective areas, representing “0”s. Whenthe read laser beam strikes the areas, it is reflected directly to thelight-sensitive diode of the read head, creating an electrical currentthat is sent to the controller in the disk drive. The controllerinterprets the pattern of electrical pulses, decodes the data that theyrepresent, checks the data for error, and sends the data to a computer.

[0008] To erase data or to change a mark back to crystalline phase, thedisk drives use a lower-energy laser beam to heat marked areas to arelatively low temperature. This amount of heat is below the meltingpoint of the phase-change material, but it still loosens up the phasechange recording media so that it can recrystallize to the originalstate.

[0009] Apart from the magneto-optical media, the phase-change recordingmedia do not require the application of an external magnetic field tothe recording media, and it is possible to read, write, and erase datawith respect to the phase-change disk by only focusing a laser beamemitted by a laser diode (LD), onto the recording layer of the disk.

[0010] If an optical recording/reproducing apparatus uses a single-pulselaser driving waveform when recording data onto the phase-changerecording medium, the heating or the cooling of the recording layer ofthe disk is often likely to be insufficient for the formation ofnon-crystalline phase or crystalline phase in the recording layer, whichwill produce an undesired pattern or an error caused when reproducingthe recorded data from the recording medium. In order to eliminate theabove problem and reliably reproduce the recorded data from therecording medium without producing the undesired pattern, the opticalrecording/reproducing apparatus is required to use a multi-pulse laserdriving waveform when recording data onto the phase-change recordingmedium.

[0011] A mark portion of the multi-pulse laser driving waveform includesa head-end high-level signal portion, a plurality of subsequenthigh-level signal portions, and a plurality of intermediate low-levelsignal portions between the high-level signal portions. The head-end andsubsequent high-level of the drive current correspond to a peak power“Pw” for the laser beam of the laser diode to heat the recording layerof the disk to a high temperature above the melting point of thephase-change material. The intermediate low level of the drive currentcorresponds to a bottom power “Pb” for the laser beam of the laser diodeto cool the recording layer of the disk. Suppose that a read-processpower for the laser beam of the laser diode during the reading processis represented by “Pr”. The peak power “Pw”, the bottom power “Pb” andthe read-process power “Pr” are predetermined such that they satisfy thefollowing conditions.

Pw>Pb=Pr   (1)

[0012] A space portion of the multi-pulse laser driving waveformincludes a single middle-level signal portion. The middle level of thedrive current corresponds to an erase power “Pe” for the laser beam ofthe laser diode to erase the data in the recording layer of the disk.The erase power “Pe” is predetermined such that it satisfies thefollowing conditions.

Pw>Pe>Pb   (2)

[0013] When the optical recording/reproducing apparatus uses theabove-described multi-pulse laser driving waveform when recording dataonto the phase-change recording medium, it is possible to eliminate theproblem of the single-pulse laser driving waveform and reliablyreproduce the recorded data from the recording medium without producingthe undesired pattern.

[0014] Further, when recording data onto the phase-change recordingmedium, the optical recording/reproducing apparatus is required toproperly carry out the laser power control.

[0015] Generally, the laser diodes have the light vs. currentcharacteristics. The light output is relatively small until the currentreaches a threshold current. Thereafter the optical intensity risesapproximately linearly with increasing current. For digital modulation,the current to the laser diodes switches between two levels, the 0 levelcurrent being near the threshold current and the 1 level current beinghigher. The problems associated with typical laser diodes are that thecharacteristic curve bends over at high current and tends to shift andbend to the right with increasing temperature.

[0016] A method for stabilizing the optical power of a laser diode isthe automatic power control (APC). The optical recording/reproducingapparatus usually executes the APC process to stabilize the opticalpower of the laser diode.

[0017] When the APC process is performed, part of the laser beam emittedby the laser diode is received at a photodetector (PD), and thephotodetector outputs a monitoring current the amplitude of which isproportional to the optical power of the laser beam. By utilizing themonitoring current output by the photodetector, the drive current to thelaser diode is controlled in the APC process.

[0018] When the APC process is performed for the reading of thephase-change recording medium, a high-frequency current is superimposedon the drive current to the laser diode so as to reduce the noises. Thedrive current can be assumed as being a constant current. By providing afeedback loop having frequencies that are within a relatively lowfrequency range, the APC process can be performed.

[0019] When the APC process is performed for the writing of the opticalrecording media, the recording power of the laser diode is quicklyshifted between the different levels in order for the formation of marksand spaces in the recording layer of the disk. Some corrective measuresmust be taken for the APC process.

[0020] For CD and DVD media, the requirement that a digital sum value(DSV) of the recording data should be set to zero is met. By providing afeedback loop with the limited bandwidth that is within a relatively lowfrequency range, the APC process for the writing of the recording media,which is essentially the same as the APC process for the reading of therecording media, can be performed with a simple configuration of theoptical recording/reproducing apparatus. However, it is difficult toprovide accurate power control for the optical power of the laser diodeduring the writing.

[0021] For the CD-R media, the write pulse strategy shown in FIG. 11 isused by a conventional optical recording/reproducing apparatus. Thewriting of the CD-R media is performed with the write pulse strategyshown in FIG. 11. When a mark or a space having a maximum length of 11T(T indicates a unit length corresponding to a period of a channel clock)is recorded on the disk, the output power of the laser diodecorresponding to each of the mark and the space is sampled and held bythe sample/hold circuit. Even when the speed of the disk rotation is setat the quadruple speed, the required bandwidth of the photodetector andamplifier in the light-receiving module is only several MHz. It ispossible to provide accurate power control by using a configuration ofthe optical recording/reproducing apparatus with a relatively low cost.

[0022] For the DVD-rewritable media, it is desirable to perform theabove-mentioned multi-pulse laser driving. If a sample/hold circuit isused to detect the peak power of the laser diode, the required bandwidthof the light receiving module and the subsequent processing circuitsbecomes very large, which will not be appropriate for practical use.

[0023] However, a sample/hold circuit may be used to detect the erasepower of the laser diode when a long space data is recorded on the disk.By using this method, the detection of the erase power is possible.

[0024] Further, there is a method for controlling the bottom power orthe peak power of the laser diode. In this method, in order to suitablycontrol the bottom power or the peak power of the laser diode, aderivative efficiency of the laser diode may be initially calculatedprior to the start of the recording process so that the current, derivedfrom the calculated derivative efficiency, is added to or reduced fromthe bottom-level drive current used to produce the erase power, so as toobtain the peak-level drive current for the peak power of the laserdiode.

[0025] The above-mentioned method is effective only when the derivativeefficiency of the laser diode does not change and is maintained at aconstant level. If the derivative efficiency varies, the error of thepeak-level drive current obtained by using the above method will not benegligible.

[0026] As disclosed in Japanese Laid-Open Patent Application No.9-171631, there is known an optical recording/reproducing apparatus thatdetects the peak-power optical output of the laser diode when it isdriven at the peak-level drive current in a non-pulse condition. In theabove-mentioned conventional apparatus, the peak-power laser beam whenthe laser diode is driven at the peak-level drive current in thenon-pulse condition is detected, and the erase-power laser beam when aspace is recorded on the disk is detected, and then the bottom-leveldrive current to the laser diode is corrected by using the detected peakpower and the detected erase power. The laser diode is driven at thecorrected bottom-level drive current to produce the bottom-level opticaloutput.

[0027] Generally, it is necessary that the optical recording/reproducingapparatus always maintain the three recording power levels, includingthe peak power, the erase power and the bottom power for the laserdiode, in order to obtain the optical waveform with good jittercharacteristics when the data is reproduced from the phase-changerecording medium.

[0028] However, when the above-described laser power control of theconventional apparatus is applied to the write pulse strategy for theDVD-rewritable media, there is a problem in that the formation of a markon the recording layer of the disk when the laser diode is driven at thepeak-level drive current in the non-pulse condition becomes deficient.

SUMMARY OF THE INVENTION

[0029] In order to overcome the problems described above, preferredembodiments of the present invention provide an improved opticalrecording/reproducing apparatus that can maintain the accurate recordingpower levels of the laser diode optical power, including the peak power,the erase power and the bottom power, even when the light receivingmodule with the limited bandwidth is used, and does not cause thedeficient formation of a mark on the disk when recording data onto thedisk.

[0030] According to one preferred embodiment of the present invention,an optical recording/reproducing apparatus records a sequence of datablocks onto an optical recording medium by using a laser driving currentwaveform to control emission of a laser beam by a semiconductor laser,and reproduces the data blocks from the medium, the waveform including asequence of mark and space data portions each having a data length thatcorresponds to a multiple of a period of a channel clock based on arecording data modulation method, the optical recording/reproducingapparatus comprising: a semiconductor laser driver which supplies aselected one of a plurality of drive currents, including a first-leveldrive current and a second-level drive current, to the semiconductorlaser to control the emission of a laser beam by the laser; a currentdriver which selectively outputs one of a plurality of incrementcurrents to the laser driver in response to control signals, theplurality of increment currents including a first increment currentsupplied to the laser driver during an automatic power control processand a second increment current supplied to the laser driver during aspecial power setting process; a detection unit which detects a firstpower sample signal, at a first sampling point of the waveform, from thelaser beam emitted when the first increment current is supplied to thelaser driver, and detects a second power sample signal, at a secondsampling point of the waveform, from the laser beam emitted when thesecond increment current is supplied to the laser driver; and acalculation unit which calculates a derivative efficiency of the laserbased on the first and second power sample signals detected by thedetection unit, so that the drive currents of the laser driver, suppliedto the laser, are controlled based on the calculated derivativeefficiency.

[0031] According to another preferred embodiment of the presentinvention, the above-mentioned optical recording/reproducing apparatusincludes the current driver that is configured into an erase-levelcurrent driver which selectively outputs one of a plurality oferase-level increment currents to the laser driver in response toerase-level control signals, the plurality of erase-level incrementcurrents including a first erase-level increment current supplied to thelaser driver during the automatic power control process and a seconderase-level increment current supplied to the laser driver during thespecial power setting process.

[0032] According to another preferred embodiment of the presentinvention, the above-mentioned optical recording/reproducing apparatusincludes the current driver that is configured into a space-levelcurrent driver that selectively outputs one of a plurality ofspace-level increment currents to the laser driver in response tospace-level control signals, the plurality of space-level incrementcurrents including a first space-level increment current supplied to thelaser driver during the automatic power control process and a secondspace-level increment current supplied to the laser driver during thespecial power setting process.

[0033] According to another preferred embodiment of the presentinvention, the above-mentioned optical recording/reproducing apparatusincludes the current driver that is configured into a bottom-levelcurrent driver that selectively outputs one of a plurality ofbottom-level increment currents to the laser driver in response tobottom-level control signals, the plurality of bottom-level incrementcurrents including a first bottom-level increment current supplied tothe laser driver during the automatic power control process and a secondbottom-level increment current supplied to the laser driver during thespecial power setting process, the second bottom-level increment currentsupplied to the laser driver resulting in a drive current produced bythe laser driver, which is equal to a peak-level drive current to thelaser.

[0034] According to another preferred embodiment of the invention, anoptical recording/reproducing apparatus records a sequence of datablocks onto an optical recording medium by using a laser driving currentwaveform to control emission of a laser beam by a semiconductor laser,and reproduces the data blocks from the medium, the waveform including asequence of mark and space data portions each having a data length thatcorresponds to a multiple of a period of a channel clock based on arecording data modulation method, the optical recording/reproducingapparatus comprising: a semiconductor laser driver which supplies aselected one of a plurality of drive currents, including at least abias-level drive current and a peak-level drive current, to thesemiconductor laser to control the emission of a laser beam by thelaser; a bias-level current driver which selectively outputs one of aplurality of bias-level drive currents to the laser driver in responseto control signals, the plurality of bias-level drive currents includinga first drive current supplied to the laser driver during an automaticpower control APC process and a second drive current supplied to thelaser driver during an automatic current control ACC process; and acontrol unit which selectively executes one of the APC process and theACC process on the current driver by supplying the control signals tothe current driver, the control unit outputting a sampling signal to thecurrent driver in response to a power-monitor signal of the laser beamemitted by the laser when recording data onto the recording medium,wherein, when the control unit outputs the sampling signal within apredetermined time, the control unit continuously executes the APCprocess on the current driver so that the current driver supplies thefirst drive current to the laser driver, and when the control unit doesnot output the sampling signal over a period exceeding the predeterminedtime, the control unit terminates the execution of the APC process andstarts the execution of the ACC process by using a switching unit thatoperates in response to the control signals supplied to the currentdriver, so that the current driver supplies the second drive current tothe laser driver.

[0035] In the optical recording/reproducing apparatus of the presentinvention, the first power sample signal at the first sampling point ofthe waveform is detected from the laser beam emitted when the firstincrement current is supplied to the laser driver, and the second powersample signal at the second sampling point of the waveform is detectedfrom the laser beam emitted when the second increment current issupplied to the laser driver. Then, the derivative efficiency of thelaser is calculated based on the first and second power sample signalsin accordance with predetermined equations, so that the drive currentsof the laser driver, supplied to the laser, are controlled based on thecalculated derivative efficiency. The optical recording/reproducingapparatus of the present invention can provide accurate calculation ofthe derivative efficiency with little calculation errors and prevent thedeterioration of the overwriting characteristics and the deficiency ofthe erasing.

[0036] Further, in the optical recording/reproducing apparatus of thepresent invention, the drive currents supplied to the laser arecontrolled based on the calculated derivative efficiency in anappropriate manner. Accordingly, the optical recording/reproducingapparatus of the present invention is effective in maintaining theaccurate recording power levels of the laser optical power, includingthe peak power, the erase or space power and the bottom power, even whenthe light-receiving module with the limited bandwidth is used. Theoptical recording/reproducing apparatus of the present invention iseffective in preventing the deficient formation of a mark on therecording medium when recording data onto the disk as in theconventional apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other objects, features and advantages of the present inventionwill become apparent from the following detailed description when readin conjunction with the accompanying drawings.

[0038]FIG. 1 is a block diagram of one preferred embodiment of theoptical recording/reproducing apparatus of the invention.

[0039]FIG. 2 is a block diagram of an erase-level current driver in theoptical recording/reproducing apparatus of FIG. 1.

[0040]FIG. 3 is a waveform diagram for explaining a multi-pulse laserdriving waveform of the optical recording/reproducing apparatus of FIG.1 during a writing process.

[0041]FIG. 4 is a time chart for explaining exemplary waveforms of theoutput signals of the elements of the optical recording/reproducingapparatus of FIG. 1 during a special power setting process.

[0042]FIG. 5A, FIG. 5B and FIG. 5C are diagrams for explaining examplesof the detection of erase-level optical power at two sampling pointsused by the optical recording/reproducing apparatus of FIG. 1.

[0043]FIG. 6 is a time chart for explaining exemplary waveforms of theoutput signals of the elements of the optical recording/reproducingapparatus of FIG. 1.

[0044]FIG. 7 is a diagram for explaining a laser diode derivativeefficiency used by the optical recording/reproducing apparatus of FIG.1.

[0045]FIG. 8 is a diagram for explaining an example of the calculationof the derivative efficiency used by the optical recording/reproducingapparatus of FIG. 1.

[0046]FIG. 9 is a diagram for explaining the light vs. currentcharacteristics of the laser diode with a variation of the derivativeefficiency during the writing mode.

[0047]FIG. 10 is a time chart for explaining exemplary waveforms of theoutput signals of the elements of the optical recording/ reproducingapparatus of FIG. 1.

[0048]FIG. 11 is a waveform diagram for explaining a write pulsestrategy used by a conventional optical recording/reproducing apparatus.

[0049]FIG. 12A and FIG. 12B are waveform diagrams for explaining thebasic concepts of the optical recording/reproducing apparatus of theinvention.

[0050]FIG. 13 is a block diagram of another preferred embodiment of theoptical recording/reproducing apparatus of the invention.

[0051]FIG. 14 is a block diagram of a bottom-level current driver in theoptical recording/reproducing apparatus of FIG. 13.

[0052]FIG. 15 is a time chart for explaining exemplary waveforms of theoutput signals of the elements of the optical recording/reproducingapparatus of FIG. 13.

[0053]FIG. 16 is a time chart for explaining the waveforms of outputsignals of various elements of the optical recording/reproducingapparatus of FIG. 13 during an efficiency calculation process.

[0054]FIG. 17 is a diagram for explaining the light vs. currentcharacteristics of a laser diode in the optical recording/reproducingapparatus of FIG. 13.

[0055]FIG. 18 is a diagram for explaining the light vs. currentcharacteristics of the laser diode with a variation of the derivativeefficiency during the writing mode.

[0056]FIG. 19 is a block diagram of another preferred embodiment of theoptical recording/reproducing apparatus of the invention.

[0057]FIG. 20 is a block diagram of a space-level current driver in theoptical recording/reproducing apparatus of FIG. 19.

[0058]FIG. 21 is a time chart for explaining the waveforms of outputsignals of the elements of the optical recording/reproducing apparatusof FIG. 19 during the normal writing mode and during the efficiencycalculation mode.

[0059]FIG. 22 is a block diagram of another preferred embodiment of theoptical recording/reproducing apparatus of the invention.

[0060]FIG. 23 is a circuit diagram of a bias-level current driver in theoptical recording/reproducing apparatus of FIG. 22.

[0061]FIG. 24 is a time chart for explaining exemplary waveforms of theoutput signals of the CPU of the optical recording/reproducing apparatusof FIG. 22.

[0062]FIG. 25 is a diagram for explaining a relationship between thelaser drive current and the laser optical power.

[0063]FIG. 26 is a time chart for explaining operations of thebias-level current driver of the present embodiment during an automaticcurrent control process.

[0064]FIG. 27 is a time chart for explaining exemplary waveforms of theoutput signals of one alternative embodiment of the opticalrecording/reproducing apparatus of FIG. 22.

[0065]FIG. 28 is a time chart for explaining exemplary waveforms of theoutput signals of another alternative embodiment of the opticalrecording/reproducing apparatus of FIG. 22.

[0066]FIG. 29 is a block diagram of a counter in the opticalrecording/reproducing apparatus of the embodiment of FIG. 28.

[0067]FIG. 30 is a block diagram of another preferred embodiment of theoptical recording/reproducing apparatus of the invention.

[0068]FIG. 31 is a circuit diagram of a bias-level current driver in theoptical recording/reproducing apparatus of FIG. 30.

[0069]FIG. 32 is a circuit diagram of an erase-level current driver inthe optical recording/reproducing apparatus of FIG. 30.

[0070]FIG. 33 is a waveform diagram for explaining a multi-pulse laserdrive waveform of the optical recording/reproducing apparatus of FIG.30.

[0071]FIG. 34 is a time chart for explaining exemplary waveforms of theoutput signals of the CPU of the optical recording/reproducing apparatusof FIG. 30.

[0072]FIG. 35 is a diagram for explaining a laser diode derivativeefficiency used by the optical recording/reproducing apparatus of FIG.30.

[0073]FIG. 36 is a diagram for explaining the optical power vs. drivecurrent characteristics of the laser diode in the opticalrecording/reproducing apparatus of FIG. 30.

[0074]FIG. 37 is a time chart for explaining exemplary waveforms of theoutput signals of the elements of the optical recording/reproducingapparatus of FIG. 30.

[0075]FIG. 38 is a diagram for explaining an example of detection oferase-level optical power at two sampling points used by the opticalrecording/reproducing apparatus of FIG. 30.

[0076]FIG. 39 is a diagram for explaining a calculation of a laser diodederivative efficiency that is performed by the opticalrecording/reproducing apparatus of FIG. 30.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0077] A description will be provided of preferred embodiments of thepresent invention with reference to the accompanying drawings.

[0078]FIG. 1 shows one preferred embodiment of the opticalrecording/reproducing apparatus of the invention. FIG. 3 shows amulti-pulse laser driving of the optical recording/reproducing apparatusof FIG. 1 during a normal writing process.

[0079] In the optical recording/reproducing apparatus of the presentembodiment, DVD-format code data is recorded onto a DVD-rewritable disk(or a phase-change recording medium) by focusing a laser beam emitted bya laser diode, on the recording layer of the disk. The recorded data isreproduced from the disk by the optical recording/reproducing apparatus.The optical recording/reproducing apparatus of the present embodimentemploys the eight-to-sixteen modulation (ESM) scheme as the datamodulation method in order to carry out the pulse-width modulation (PWM)recording process for the DVD-rewritable disk.

[0080] In the optical recording/reproducing apparatus of FIG. 1, themulti-pulse drive current in which data is modulated is supplied to thelaser light source, and the laser light source emits the laser beam tothe DVD-rewritable disk. A stream of data blocks, including marks andspaces, are recorded onto the recording layer of the disk by focusingthe laser beam on the recording layer of the disk. The followingdescription deals with only the configuration and the writing process ofthe optical recording/reproducing apparatus of the present embodiment,and a description of the configuration and the reproducing processthereof will be omitted, for the sake of simplicity.

[0081] Generally, when recording data onto the phase-change recordingmedia by using the multi-pulse laser driving, the opticalrecording/reproducing apparatus is required to maintain the accuratepower levels of the laser optical power, including the peak power (Pw)corresponding to the peak-level drive current, the bottom power (Pb)corresponding to the bottom-level drive current, and the erase power(Pe) or space power corresponding to the erase-level drive current orspace-level drive current.

[0082] In order to eliminate the problem of the single pulse laserdriving waveform and reliably reproduce the recorded data from therecording medium without producing the undesired pattern, the opticalrecording/reproducing apparatus of the present embodiment uses amulti-pulse laser driving waveform, as shown by (c) in FIG. 3, whenrecording data onto the phase-change recording medium.

[0083] As shown by (c) in FIG. 3, a mark portion of the multi-pulselaser driving waveform (corresponding to the high level of the ESMsignal indicated by (b) in FIG. 3) includes a head-end high-level signalportion “A”, a plurality of subsequent high-level signal portions “B”,and a plurality of intermediate low-level signal portions “C” betweenthe high-level signal portions. The head-end and subsequent high-levelof the driving waveform (A or B) corresponds to the peak power “Pw” forthe laser beam of the laser diode to heat the recording layer of thedisk to a high temperature above the melting point of the phase-changematerial. The low level of the driving waveform (C) corresponds to thebottom power “Pb” for the laser beam of the laser diode to cool therecording layer of the disk. Suppose that a read-process power for thelaser beam of the laser diode during a reproducing period is representedby “Pr”. The peak power “Pw”, the bottom power “Pb” and the read-processpower “Pr” are predetermined so as to satisfy the conditions: Pw>Pb=Pr.

[0084] Further, as shown by (c) in FIG. 3, a space portion of themulti-pulse laser driving waveform (corresponding to the low level ofthe ESM signal indicated by (b) in FIG. 3) includes a singlemiddle-level signal portion “D”. The middle level of the drivingwaveform (D) corresponds to an erase power “Pe” for the laser beam ofthe laser diode to erase the data in the recording layer of the disk.The erase power “Pe” is predetermined such that it satisfies theconditions: Pw>Pe>Pb.

[0085] When the optical recording/reproducing apparatus of the presentembodiment uses the above-described multi-pulse laser driving waveformduring the recording period, it is possible to eliminate the problem ofthe single-pulse laser driving waveform and reliably reproduce therecorded data from the recording medium without producing the undesiredpattern.

[0086] Next, a description will be provided of the automatic powercontrol (APC) process which is performed by the opticalrecording/reproducing apparatus of the present embodiment during anormal writing process.

[0087] As shown in FIG. 1, the optical recording/reproducing apparatusof the present embodiment generally comprises a central processing unit(CPU) 1, a laser diode (LD) 2, a photodetector (PD) 3, a laser diodedriver (LDD) 4, a current-voltage converter 5, a sample/hold circuit 6,an analog-to-digital converter (ADC) 7, a bottom-level current source(BCS) 8, an erase-level current driver (ECD) 9, and a peak-level currentsource (PCS) 10.

[0088] In the optical recording/reproducing apparatus of FIG. 1, the CPU1 sets a bottom-level drive current at the output of the bottom-levelcurrent source (BCS) 8 by supplying a bottom-level control (BLC) signalto the BCS 8. The signal line through which the BLC signal is sent fromthe CPU 1 to the BCS 8 is designated by reference numeral 104. Thesignal line through which the bottom-level drive current is sent fromthe BCS 8 to the LDD 4 is designated by reference numeral 108.

[0089] The CPU 1 sets a peak-level increment current at the output ofthe peak-level current source (PCS) 10 by supplying a peak-level control(PLC) signal to the PCS 10. The signal line through which the PLC signalis sent from the CPU 1 to the PCS 10 is designated by reference numeral107. The signal line through which the peak-level increment current issent from the PCS 10 to the LDD 4 is designated by reference numeral110.

[0090] The CPU 1 sets an erase-level increment current at the output ofthe erase-level current driver (ECD) 9 by supplying an erase-levelcontrol (ELC) signal to the ECD 9. The signal line through which the ELCsignal is sent from the CPU 1 to the ECD 9 is designated by referencenumeral 105. The signal line through which the erase-level incrementcurrent is sent from the ECD 9 to the LDD 4 is designated by referencenumeral 109.

[0091] Specifically, each of the BCS 8 and the PCS 10 is configured byusing a digital-to-analog converter (DAC). The digital bottom-levelcontrol signal from the CPU 1 is received at the BCS 8, and, in responseto the control signal, the BCS 8 outputs the analog bottom-level drivecurrent to the LDD 4. The digital peak-level control signal from the CPU1 is received at the PCS 10, and, in response to the control signal, thePCS 10 outputs the analog peak-level increment current signal to the LDD4.

[0092] The ECD 9 is configured so that the ECD 9 selectively outputs oneof a plurality of erase-level increment currents to the LDD 4 throughthe signal line 109 in response to control signals supplied by the CPU1.

[0093] The LDD 4 receives the bottom-level drive current from the signalline 108, the erase-level increment current from the signal line 109 andthe peak-level increment current from the signal line 110, and, inresponse to the current signals, the LDD 4 supplies a selected one ofthe drive currents to the laser diode 2 at a time under the control ofthe CPU 1.

[0094] The CPU 1 converts a sequence of input recording data blocks intoan eight-to-sixteen modulation (ESM) signal as in the waveform indicatedby (b) in FIG. 3. The CPU 1 further generates a multi-pulse laserdriving waveform as in the waveform indicated by (c) in FIG. 3. Inaccordance with the multi-pulse laser driving waveform, the CPU 1supplies a bottom-power enable (BPE) signal, an erase-power enable (EPE)signal and a peak-power enable (PPE) signal to the LDD 4. The signalline through which the bottom-power enable (BPE) signal is sent from theCPU 1 to the LDD 4 is designated by reference numeral 101. The signalline through which the erase-power enable (EPE) signal is sent from theCPU 1 to the LDD 4 is designated by reference numeral 102. The signalline through which the peak-power enable (PPE) signal is sent from theCPU 1 to the LDD 4 is designated by reference numeral 103.

[0095] When the bottom-power enable (BPE) signal 101 is set in the highlevel (H), the LDD 4 supplies the bottom-level drive current 108 to theLD 2. The LD 2 at this time is driven by the bottom-level drive currentto output the laser beam at the bottom power (Pb). When the erase-powerenable (EPE) signal 102 is set in the high level (H), the LDD 4 suppliesa sum of the bottom-level drive current 108 and the erase-levelincrement current 109 to the LD 2. The LD 2 at this time is driven bythe erase-level drive current to output the laser beam at the erasepower (Pe). When the peak-power enable (PPE) signal 103 is set in thehigh level (H), the LDD 4 supplies a sum of the bottom-level drivecurrent 108 and the peak-level increment current 110 to the LD 2. The LD2 at this time is driven by the peak-level drive current to output thelaser beam at the peak power (Pw).

[0096]FIG. 6 shows exemplary waveforms of the output signals of theelements of the optical recording/reproducing apparatus of the presentembodiment.

[0097] As in the waveforms indicated by (b) through (d) in FIG. 6, thebottom-power enable (BPE) signal 101 is always set in the high level (H)during the recording mode. When outputting the erase power laser beam atthe LD 2, the erase power enable (EPE) signal 102 is set in the highlevel (H) at the same time. The LDD 4 supplies the sum of thebottom-level drive current 108 and the erase-level increment current 109to the LD 2. When outputting the peak power laser beam at the LD 2, thepeak power enable (PPE) signal 103 is set in the high level (H) at thesame time. The LDD 4 supplies the sum of the bottom-level drive current108 and the peak-level increment current 110 to the LD 2.

[0098] When the drive current is supplied from the LDD 4 to the LD 2,the LD 2 outputs the laser beam to the phase-change recording medium, sothat the data is recorded onto or reproduced from the recording layer ofthe phase-change recording medium. The laser beam output by the LD 2 isreceived at the photodetector (PD) 3. The PD 3 outputs a monitoringcurrent that is proportional to the laser optical power of the receivedlaser beam. The monitoring current is supplied from the PD 3 to thecurrent-voltage converter 5. The signal line through the monitoringcurrent signal is sent from the PD 3 to the current-voltage converter 5is designated by reference numeral 112.

[0099] The current-voltage converter 5 outputs a power-monitoring signalbased on the monitoring current supplied by the PD 3. The signal linethrough the power monitoring signal is sent from the current-voltageconverter 5 to the sample/hold circuit 6 is designated by referencenumeral 113. By utilizing the power-monitoring signal 113 output by thecurrent-voltage converter 5, the automatic power control (APC) processis performed by the optical recording/reproducing apparatus of thepresent embodiment.

[0100] In the optical recording/reproducing apparatus of FIG. 1, the CPU1 is connected to the sample/hold circuit 6 through a signal line 111,and an erase-power sample timing (EPST) signal is sent from the CPU 1 tothe sample/hold circuit 6 through the signal line 111. When a long spacehaving a maximum data length (in a case of the ESM scheme, 14T) isformed on the disk by the laser beam of the LD 2 during the recordingmode, the CPU 1 sets the erase-power sample timing (EPST) signal in thehigh level (H). When the EPST signal is set in the high level (H), thepower-monitoring signal 113 is sampled and held by the sample/holdcircuit 6. The ADC 7 converts the power-monitoring signal, held by thesample/hold circuit 6, into a digital erase-power sample (EPS) signal.The EPS signal is supplied from the ADC 7 to the CPU 1 through a signalline 114. See the waveforms indicated by (f) through (h) in FIG. 6.

[0101] The EPS signal output by the ADC 7 is received at the CPU 1, andthe CPU 1 compares the received EPS signal with a reference value. TheCPU 1 corrects the erase-level control (ELC) signal 105, which issupplied to the erase-level current driver (ECD) 9, based on adifference between the EPS signal and the reference value. As thecorrected ELC signal 105 is supplied to the ECD 9, the ECD 9 supplies acorrected erase-level increment current to the LDD 4 so that the erasepower (Pe) of the laser optical output is maintained at a proper level.The LD 2 at this time is driven by the corrected erase-level drivecurrent supplied by the LDD 4, so as to output the laser beam at theproper erase power (Pe).

[0102] Further, in the present embodiment, the CPU 1 calculates abottom-level drive current “Ib” and a peak-level drive current “Iw”based on the corrected erase-level drive current and a derivativeefficiency, which will be described in greater detail below.

[0103]FIG. 7 shows a laser diode derivative efficiency used by theoptical recording/reproducing apparatus of the present embodiment.

[0104] Hereinafter, the derivative efficiency “η” of the LD 2 used bythe optical recording/reproducing apparatus of the present embodiment,is defined as being a gradient ΔP/ΔI of the light vs. currentcharacteristic curve as shown in FIG. 7.

[0105] Suppose that the bottom-level drive current corresponding to thebottom power Pb, the erase-level drive current corresponding to theerase power Pe, and the peak-level drive current corresponding to thepeak power Pw are represented by “Ib”, “Ie”, and “Iw”, respectively. Asis apparent from the light vs. current characteristic curve of FIG. 7,the bottom power “Pb” and the peak power “Pw” are represented by thefollowing equations.

Pe=Pe—η×(Ie—Ib)   (3)

Pw=Pe+η×(Iw—Ie)   (4)

[0106] From the above equations (3) and (4), the bottom-level drivecurrent “Ib” and the peak-level drive current “Iw” can be calculated inaccordance with the following equations.

Ib=Ie—(Pe—Pb)/η  (5)

Iw=Ie+(Pw—Pe)/η  (6)

[0107] In this case, the derivative efficiency “η” of the LD 2 ispredetermined, and the calculation of the bottom-level drive current Iband the peak-level drive current Iw is performed by using thepredetermined derivative efficiency. As described above, the CPU 1calculates the bottom-level drive current “Ib” and the peak-level drivecurrent “Iw” based on the corrected erase-level drive current and thederivative efficiency. Thereafter the CPU 1 sets the bottom-levelcontrol signal 104 and the peak-level control signal 107, which arerespectively supplied to the bottom-level current source 8 and thepeak-level current source 10, to the proper values based on thecalculated drive currents “Ib” and “Iw”.

[0108] As described above, the LDD 4 supplies the sum of thebottom-level drive current 108 and the erase-level increment current 109to the LD 2. Also, the LDD 4 supplies the sum of the bottom-level drivecurrent 108 and the peak-level increment current 110 to the LD 2.Suppose that the erase-level increment current 108 and the peak-levelincrement current 110 are represented by “ΔIe” and “ΔIw”, respectively.As is apparent from the characteristic curve shown in FIG. 7, theerase-level drive current “Ie” and the peak-level drive current “Iw” canbe calculated in accordance with the following equations.

Ie=Ib+ΔIe   (7)

Iw=Ib+ΔIw   (8)

[0109] In the present embodiment, a time period for which theabove-described APC process is performed is shorter than a time periodfor which a special power setting process (which will be describedlater) is performed. For example, in the present embodiment, the erasepower sample signal 114, output by the ADC 7, is received by the CPU 1when a long space having a maximum data length (14T) is formed on thedisk by the laser beam of the LD 2. As described above, at this time,the erase-power sample timing (EPST) signal is set in the high level bythe CPU 1.

[0110] According to the DVD standards, the data length 14T of a longspace is equal to the data length of a sync code in the sequence of theinput recording data blocks, and the sampling and holding of the erasepower in the APC process will be performed once for every two syncframes (1488T).

[0111] Strictly speaking, either a mark having the maximum data length14T or a space having the maximum data length 14T is selected so as tomeet the requirement that the digital sum value (DSV) be equal to zero.The sampling and holding of the erase power in the APC process is notalways performed once for every two sync frames (1488T). However, forthe sake of simplicity, it is assumed that, in the present embodiment, amark having the data length 14T and a space having the data length 14Tare alternately selected with equal probabilities.

[0112] In the optical recording/reproducing apparatus of the presentembodiment, the CPU 1 calculates the bottom-level drive current “Ib” andthe peak-level drive current “Iw” based on the corrected erase-leveldrive current (obtained when forming a long space having the maximumdata length 14T on the disk by the laser beam of the LD 2) and thepredetermined derivative efficiency. Accordingly, the opticalrecording/reproducing apparatus of the present embodiment is effectivein maintaining the accurate recording power levels of the laser opticalpower, including the peak power, the erase power and the bottom power,even when the light-receiving module with the limited bandwidth is used.

[0113]FIG. 9 shows the light vs. current characteristics of the laserdiode with a variation of the derivative efficiency during the writingmode.

[0114] As shown in FIG. 9, the light vs. current characteristic curvetends to shift and bend to the right with increasing temperature, andthe derivative efficiency of the laser diode tends to vary withincreasing temperature. If the derivative efficiency varies, the errorsof the calculated bottom-level drive current “Ib” and the calculatedpeak-level drive current “Iw” will not be negligible.

[0115] As previously described, the conventional apparatus, disclosed inJapanese Laid-Open Patent Application No. 9-171631, carries out thepower control process in which the bottom-level drive current to thelaser diode is corrected by using the detected peak power and thedetected erase power, in order to take measures against a variation ofthe derivative efficiency. However, according to the above-mentionedpower control process, a problem arises in that the formation of a markon the recording layer of the disk when the laser diode is driven at thepeak-level drive current in the non-pulse condition becomes deficient.

[0116] In order to eliminate the above problem of the conventionalapparatus, the optical recording/reproducing apparatus of the presentembodiment is configured so that the erase-level current driver (ECD) 9selectively outputs one of the plurality of erase-level incrementcurrents to the LDD 4 through the signal line 109 in response to thecontrol signals supplied by the CPU 1. The respective power levels ofthe laser optical power when the individual erase-level incrementcurrents are supplied to the LDD 4 are sampled and held by thesample/hold circuit 6, and the corresponding erase power sample (EPS)signals are received at the CPU 1. Then, the CPU 1 calculates aderivative efficiency of the LD 2 based on the erase power samples(EPS).

[0117] Next, a description will be provided of the special power settingprocess executed by the optical recording/reproducing apparatus of thepresent embodiment with reference to FIG. 2, FIG. 4 and FIG. 5A.

[0118]FIG. 2 shows an erase-level current driver in the opticalrecording/reproducing apparatus of FIG. 1. FIG. 4 shows exemplarywaveforms of the output signals of the elements of the opticalrecording/reproducing apparatus of FIG. 1 during the special powersetting process.

[0119] As shown in FIG. 2, the erase-level current driver (ECD) 9 in thepresent embodiment generally comprises a first digital-to-analogconverter (DAC) 92, a second digital-to-analog converter (DAC) 93, and aswitch 94. The switch 94 has a high-level state and a low-level state.The erase-level select (ELS) signal output by the CPU 1 is sent to theswitch 94 through the signal line 115, and one of the high-level (H)state and the low-level (L) state is selected at the switch 94 inaccordance with the erase-level select (ELS) signal 115 supplied by theCPU 1.

[0120] The first DAC 92 has an input connected to the signal line 105and an output connected to the switch 94. When the high-level (H) stateof the switch 94 is selected according to the ELS signal 115, the ECD 9supplies an output signal of the first DAC 92 to the LDD 4 through thesignal line 109. The second DAC 93 has an input connected to the signalline 106 and an output connected to the switch 94. When the low-level(L) state of the switch 94 is selected according to the ELS signal 115,the ECD 9 supplies an output signal of the second DAC 93 to the LDD 4through the signal line 109.

[0121] The normal erase-level control (ELC) signal, which is sentthrough the signal line 105 by the CPU 1 when producing the normal erasepower (Pe) of the laser optical output, is received at the first DAC 92,and, in response to the normal ELC signal, the DAC 92 outputs the normalerase-level increment current (EIC) to the switch 94. Usually when theerase power (Pe) of the laser optical output is produced, the high-level(H) state of the switch 94 is selected according to the ELS signal 115.

[0122] A second erase-level control (ELC) signal, which is sent throughthe signal line 106 by the CPU 1 during the special power settingprocess, is received at the second DAC 93, and, in response to thesecond ELC signal, the DAC 93 outputs a second erase-level incrementcurrent (EIC) to the switch 94.

[0123] In the present embodiment, the frequency at which the executionof the special power setting process is initiated by the CPU 1 issmaller than the frequency at which the execution of the normal APCprocess is initiated by the CPU 1. An optimal value of the frequency ofexecution of the special power setting process may be experimentallydetermined depending on time-dependent variations of the derivativeefficiency of the LD 2.

[0124] At a start of the special power setting process, the CPU 1 sendsa second ELC signal 106 to the second DAC 93, and the second DAC 93outputs a second EIC to the switch 94. The low-state (L) of the switch94 is selected according to the ELS signal 115, and the second EIC,supplied by the ECD 9, results in a first erase power “Pe+α” of thelaser beam of the LD 2. See the state (2) indicated in FIG. 4.

[0125] In the above-described condition, when recording a 14T space data“14TS” onto the disk, the CPU 1 sets the ELS signal 115 in the low state(L), and the DAC 93 supplies the second EIC to the LDD 4 through thesignal line 109. Hence, only during the 14T period, the first erasepower “Pe+α” of the laser beam of the LD 2 is produced.

[0126] In the above-described condition, a corresponding first erasepower sample (EPS) signal 114, output by the ADC 7, is received by theCPU 1. The CPU 1 stores the received EPS signal in a portion of thememory that is different from a memory portion in which the EPS signalobtained during the APC process is stored.

[0127] Immediately after the 14T space data is recorded onto the disk,the CPU 1 sets the ELS signal 115 in the high state (H). The high state(H) of the switch 94 is selected according to the ELS signal 115 so asto produce the normal erase power “Pe” of the laser beam of the LD 2.See the state (3) indicated in FIG. 4.

[0128] Usually, the peak power and the erase power of the laser diodeare set to the optimal values when performing a laser power calibrationon the phase-change recording disk, so as to retain good jittercharacteristics when reproducing the data from the disk. If an erasepower of the laser beam of the LD 2, different from the normal erasepower Pe, is produced for a too long time, the jitter characteristicswill deteriorate. In the present embodiment, immediately after the 14Tspace data is formed on the disk with the first erase power, the switch94 is returned to the high state (H) so as to produce the normal erasepower. Hence, the deterioration of the jitter characteristics will benegligible.

[0129] Following the above state (3), the CPU 1 sends another second ELCsignal 106 to the second DAC 93, and the second DAC 93 outputs anothersecond EIC to the switch 94. The low-state (L) of the switch 94 isselected according to the ELS signal 115, and the second EIC, suppliedby the ECD 9, results in a second erase power “Pe—α” of the laser beamof the LD 2. See the state (4) indicated in FIG. 4.

[0130] In the above-described condition, when recording a 14T space data“14TS” onto the disk, the CPU 1 sets the ELS signal 115 in the low state(L), and the DAC 93 supplies the second EIC to the LDD 4 through thesignal line 109. Hence, only during the 14T period, the second erasepower “Pe—α” of the laser beam of the LD 2 is produced.

[0131] In the above-described condition, a corresponding second erasepower sample (EPS) signal 114, output by the ADC 7, is received at theCPU 1. The CPU 1 stores the received second EPS signal in anotherportion of the memory that is different from the memory portion in whichthe EPS signal obtained during the APC process is stored.

[0132] Immediately after the 14T space data is recorded onto the disk,the CPU 1 sets the ELS signal 115 in the high state (H). The high state(H) of the switch 94 is selected according to the ELS signal 115 so asto produce the normal erase power “Pe” of the laser beam of the LD 2.See the state (5) indicated in FIG. 4.

[0133] The CPU 1 calculates a derivative efficiency “η” of the LD 2based on the first and second erase-power sample (EPS) signals (Pe +α,Pe—α) and the corresponding erase-level drive currents (I″, I′), inaccordance with the following equation. $\begin{matrix}\begin{matrix}{\eta = {\left\{ {\left( {{Pe} + \alpha} \right) - \left( {{Pe} - \alpha} \right)} \right\}/\left( {I^{\prime\prime} - I^{\prime}} \right)}} \\{= {2{\alpha/\left( {I^{\prime\prime} - I^{\prime}} \right)}}}\end{matrix} & (9)\end{matrix}$

[0134] See the light vs. current characteristics shown in FIG. 8, for anexample of the calculation of the derivative efficiency used by thepresent embodiment at this time.

[0135] If the setting of the second DAC 93 for the second erase-poweroutput can be performed timely, the first erase-power “Pe+α” laserdriving and the second erase-power “Pe—α” laser driving may be performedwithin a period the 14T space data is output. Alternatively, anintermediate period of the 14T space data output at the normal erasepower level may be interposed between the period of the firsterase-power “Pe+α” laser driving and the period of the seconderase-power “Pe—α” laser driving. In either case, in order to calculatean accurate derivative efficiency, the first and second erase-powerlaser driving must be performed within a comparatively short period.

[0136] The reason why the first erase-power “Pe+α” and the seconderase-power “Pe—α” are sampled for the calculation of the derivativeefficiency is to make use of a proper erase-level range of the laserdriving permitted for erasing data from the phase-change recordingmedium.

[0137] In a case of the phase-change disk of a certain type, the propererase-level range is, for example, 3 mW≦Pe≦8 mW. If data on the disk iserased at a power higher than the upper limit of the proper erase-levelrange, the overwriting characteristics will deteriorate and therecording layer of the disk will be damaged. If data on the disk iserased at a power lower than the lower limit of the proper erase-levelrange, the overwriting characteristics will deteriorate and thedeficiency of the erasing will occur.

[0138] Usually, the erase power of the laser diode with respect to thephase-change recording disk is set to the optimal value when performinga laser power calibration process on the disk. The optimal value of theerase power, which is set by the laser power calibration process,normally lies around at the middle point of the proper erase-level rangeof the disk.

[0139] In order to obtain an accurate derivative efficiency of the laserdiode with a smaller calculation error, it is desirable to make thedifference between the erase-power levels at the two sampling points aslarge as possible.

[0140] In the above-described embodiment, the first erase-power “Pe +α”and the second erase-power “Pe—α”, which fall within the propererase-level range, are sampled and the derivative efficiency iscalculated accordingly. The optical recording/reproducing apparatus ofthe present embodiment can provide accurate calculation of thederivative efficiency with little calculation errors and prevent thedeterioration of the overwriting characteristics and the deficiency ofthe erasing.

[0141] In an exemplary case of the special power setting process, thevalue of α is equal to 1.5 mW where the proper erase-level range is 3mW≦Pe≦8 mW, and the erase power is Pe=6 mW.

[0142] Further, in the present embodiment, the CPU 1 calculates thebottom power “Pb” and the peak power “Pw” based on the above-calculatedderivative efficiency in a manner similar to the above-described APCprocess. Accordingly, the optical recording/reproducing apparatus of thepresent embodiment is effective in maintaining the accurate recordingpower levels of the laser optical power, including the peak power Pw,the erase power Pe and the bottom power Pb, even when the lightreceiving module with the limited bandwidth is used. The opticalrecording/reproducing apparatus is effective in preventing the deficientformation of a mark on the disk when recording data onto the disk.

[0143] Further, the optical recording/reproducing apparatus of thepresent embodiment is configured so that the erase-level current driver(ECD) 9 selectively outputs one of the plurality of erase-levelincrement currents to the LDD 4 through the signal line 109 in responseto the control signals supplied by the CPU 1. The respective powerlevels of the laser optical power when the individual erase-levelincrement currents are supplied to the LDD 4 are sampled and held by thesample/hold circuit 6, and the corresponding erase power sample (EPS)signals are received by the CPU 1. Then, the CPU 1 calculates aderivative efficiency of the LD 2 based on the erase power samples (EPS)at the plural sampling points. Therefore, the opticalrecording/reproducing apparatus of the present embodiment is effectivein maintaining the accurate recording power levels of the laser opticalpower even when the light-receiving module with the limited bandwidth isused. The optical recording/reproducing apparatus is effective inpreventing the deficient formation of a mark on the disk when recordingdata onto the disk.

[0144] Further, the optical recording/reproducing apparatus of thepresent embodiment is configured so that one of the plurality oferase-level increment currents, supplied from the ECD 9 to the LDD 4, ischanged to another during a period a space data having a data lengthlonger than a predetermined time is formed on the medium, and theerase-level increment current is returned to the original erase-levelincrement current immediately after an end of the period. Therefore, thedeterioration of the jitter characteristics will be negligible.

[0145] Further, the optical recording/reproducing apparatus of thepresent embodiment is configured so that the first erase-power “Pe +α”and the second erase-power “Pe—α”, which are obtained by increasing ordecreasing the normal erase power “Pe” by the value of α, are sampledfor the calculation of the derivative efficiency. Therefore, it ispossible to positively utilize the proper erase-level range of the laserdriving permitted for erasing data from the recording medium.

[0146] Further, the optical recording/reproducing apparatus of thepresent embodiment is configured such that the first erase-power “Pe+α”and the second erase-power “Pe—α”, which are obtained by increasing ordecreasing the normal erase power “Pe” by the value of a, are includedin the proper erase-level range for the recording medium. The opticalrecording/reproducing apparatus of the present embodiment is effectivein preventing the deterioration of the overwriting characteristics andthe deficiency of the erasing.

[0147] Next, a description will be provided of the special power settingprocess which is executed by another preferred embodiment of the opticalrecording/reproducing apparatus of the invention with reference to FIG.SB, FIG. 5C and FIG. 10.

[0148] In the present embodiment, the configuration of the opticalrecording/reproducing apparatus is essentially the same as that of theoptical recording/reproducing apparatus shown in FIG. 1, and adescription thereof will be omitted.

[0149]FIG. 5B and FIG. 5C show the examples of the detection oferase-level optical power samples at two sampling points used by theoptical recording/reproducing apparatus of the present embodiment. FIG.10 shows the exemplary waveforms of the output signals of the elementsof the optical recording/reproducing apparatus of the presentembodiment.

[0150] When the optimal value of the erase power “Pe”, which is set bythe laser power calibration process, considerably deviates from themiddle point of the proper erase-level range of the phase-changerecording disk, the special power setting process in the previousembodiment is not effective in providing accurate calculation of thederivative efficiency of the laser diode.

[0151] The special power setting process in the present embodiment takesmeasures to eliminate the above problem of the previous embodiment. Inthe present embodiment, it is determined that a difference between thenormal erase power “Pe” and one of the upper limit or the lower limit ofthe proper erase-level range for the phase-change recording disk isbelow a reference value “d”. When the above condition is met, one of afirst erase-power “Pe+β” or a second erase-power “Pe—B” that is obtainedby increasing or decreasing the normal erase power “Pe” by apredetermined value “β” is sampled for the calculation of the derivativeefficiency. See FIG. SB and FIG. 5C for the examples of the detection oferase-level optical power samples at the two sampling points.

[0152] For the sake of simplicity of the description, it is supposedthat, in the case of FIG. 10, the difference between the normal erasepower “Pe” and the lower limit of the proper erase-level range for thephase-change recording disk is determined as being less than thereference value “d”. Namely, the case of FIG. 10 corresponds to theexample of FIG. 5B.

[0153] As shown in FIG. 10, at a start of the special power settingprocess, the CPU 1 sends a second ELC signal 106 to the second DAC 93,and the second DAC 93 outputs a second EIC to the switch 94. Thelow-state (L) of the switch 94 is selected according to the ELS signal115, and the second EIC 109, supplied by the ECD 9, results in the firsterase power “Pe+β” of the laser beam produced by the LD 2. See the state(2) indicated in FIG. 10.

[0154] In the above-described condition, when recording a 14T space data“14TS” onto the disk, the CPU 1 sets the ELS signal 115 in the low state(L), and the DAC 93 supplies the second EIC to the LDD 4 through thesignal line 109. Hence, only during the 14T period, the first erasepower “Pe+β” of the laser beam of the LD 2 is produced.

[0155] In the above-described condition, a corresponding first erasepower sample (EPS) signal 114 for the first erase power “Pe+β”, outputby the ADC 7, is received by the CPU 1. The CPU 1 stores the receivedEPS signal in a portion of the memory that is different from a memoryportion in which the EPS signal obtained during the APC process isstored.

[0156] Immediately after the 14T space data is recorded onto the disk,the CPU 1 sets the ELS signal 115 in the high state (H). The high state(H) of the switch 94 is selected according to the ELS signal 115 so asto produce the normal erase power “Pe” of the laser beam of the LD 2.See the state (3) indicated in FIG. 10.

[0157] Similar to the previous embodiment of FIG. 4, in the presentembodiment, the CPU 1 calculates a derivative efficiency “η” of the LD 2based on the normal and first erase-power sample (EPS) signals (Pe,Pe+β) and the corresponding erase-level drive currents ( I, I″), inaccordance with the above equation (9).

[0158] In the present embodiment, a relationship between thepredetermined value “β” for the special power setting process and thevalue “α” for the normal APC process is represented by the followingequation.

β=2×α  (10)

[0159] Accordingly, the CPU 1 calculates the derivative efficiency “η”of the LD 2 based on the normal and first erase-power sample (EPS)signals (Pe, Pe+β) and the corresponding erase-level drive currents (I,I″), in accordance with the above equations (9) and (10).

[0160] Further, in the case of FIG. 5C, the difference between thenormal erase power “Pe” and the upper limit of the proper erase-levelrange for the phase-change recording disk is determined as being lessthan the reference value “d”. Also, in this case, the CPU 1 in thepresent embodiment carries out the special power setting process that issimilar to the above-described special power setting process for thecase of FIG. 5B. Namely, the CPU 1 obtains the normal erase-power sample(EPS) signal (Pe), the second erase-power (EPS) sample signal (Pe—β) andthe corresponding erase-level drive currents (I, I″), and thencalculates a derivative efficiency “η” of the LD 2 based on the normaland second EPS signals (Pe, Pe—β) and the corresponding erase-leveldrive currents (I, I″), in accordance with the above equations (9) and(10).

[0161] According to the above-described embodiment, it is possible toprovide accurate calculation of the derivative efficiency of the laserdiode with little calculation errors even when the value of the erasepower “Pe” considerably deviates from the middle point of the propererase-level range of the phase-change recording disk.

[0162] The optical recording/reproducing apparatus of the presentembodiment is configured that, when the difference between the normalerase power and the upper limit of the proper erase-level range for thedisk is less than the reference value, the CPU 1 calculates a derivativeefficiency of the laser diode based on the normal and second erase powersamples (Pe, Pe—β) and the corresponding erase-level drive currents (I,I′), and when the difference between the normal erase power and thelower limit of the proper erase-level range for the disk is less thanthe reference value, the CPU 1 calculates a derivative efficiency of thelaser diode based on the normal and first erase-power samples (Pe, Pe+β)and the corresponding erase-level drive currents (I, I″). Therefore,even when the value of the erase power “Pe” considerably deviates fromthe middle point of the proper erase-level range of the phase-changerecording disk, the optical recording/reproducing apparatus of thepresent embodiment is effective in providing accurate calculation of thederivative efficiency of the laser diode with little calculation errors.

[0163] In the above-described embodiments, the erase-level currentdriver (ECD) 9 in the optical recording/reproducing apparatus comprisesthe first DAC and the second DAC for selectively outputting one of thetwo erase-level increment currents (EIC) to the LDD 4. However, thenumber of the current sources included in the ECD 9 and the number ofthe erase-level increment currents supplied to the switch 94 in theoptical recording/reproducing apparatus of the present invention are notlimited to the above embodiments. Alternatively, three or more currentsources or digital-to-analog converters may be provided in theerase-level current driver (ECD) 9 and three or more erase-levelincrement currents may be supplied from the ECD 9 to the switch 94.

[0164] Next, a description will now be provided of the basic concept ofthe optical recording/reproducing apparatus of the invention withreference to FIG. 1 and FIG. 12A.

[0165]FIG. 12A shows the basic concept of the opticalrecording/reproducing apparatus of the invention when a sequence ofrecording data blocks is recorded onto rewritable optical recordingmedia (for example, a DVD-rewritable disk). For example, theconfiguration of the optical recording/reproducing apparatus shown inFIG. 1 is used to achieve the basic concept of the invention shown inFIG. 12A.

[0166] As indicated by (c) in FIG. 12A, the semiconductor laser driver(or the LDD 4) of the optical recording/reproducing apparatus supplies aselected one of a plurality of drive currents, including a first-leveldrive current and a second-level drive current, to the semiconductorlaser (or the LD 2) to control the emission of a laser beam by thelaser.

[0167] The current driver (or the ECD 9) of the opticalrecording/reproducing apparatus selectively outputs one of a pluralityof increment currents to the laser driver in response to controlsignals, the plurality of increment currents including a first incrementcurrent supplied to the laser driver during the automatic power control(APC) process and a second increment current supplied to the laserdriver during the special power setting process.

[0168] The detection unit (or the elements 3, 5, 6 and 7 in FIG. 1)detects a first power sample signal (or the EPS signal 114), at a firstsampling point (indicated by “A” in FIG. 12A) of the waveform, from thelaser beam emitted when the first increment current (or the normal EIC)is supplied to the laser driver. The detection unit detects a secondpower sample signal (or the EPS signal 114), at a second sampling point(indicated by “B” in FIG. 12A) of the waveform, from the laser beamemitted when the second increment current (or the second EIC) issupplied to the laser driver.

[0169] The calculation unit (or the CPU 1) calculates a derivativeefficiency of the laser based on the first and second power samplesignals (the EPC signals 114) detected by the detection unit, so thatthe drive currents of the laser driver, supplied to the laser, arecontrolled based on the calculated derivative efficiency.

[0170] Next, a description will be provided of another preferredembodiment of the optical recording/reproducing apparatus of theinvention with reference to FIG. 13 through FIG. 16.

[0171]FIG. 13 shows the optical recording/reproducing apparatus of thepresent embodiment. FIG. 14 shows a bottom-level current driver in theoptical recording/reproducing apparatus of FIG. 13. FIG. 15 shows theexemplary waveforms of the output signals of the elements of the opticalrecording/reproducing apparatus of FIG. 13 during a normal recordingprocess and during a special power setting process. FIG. 16 shows thewaveforms of the output signals of various elements of the opticalrecording/reproducing apparatus of FIG. 13 during a special powersetting process.

[0172] In the present embodiment, DVD-format code data is recorded ontoan optical recording disk with a dye recording layer by focusing a laserbeam emitted by a semiconductor laser, on the recording layer of thedisk. The recorded data is reproduced from the disk by the opticalrecording/reproducing apparatus. The optical recording/reproducingapparatus of the present embodiment employs the eight-to-sixteenmodulation (ESM) scheme as the data modulation method in order to carryout the pulse-width modulation (PWM) recording process for thewrite-once medium.

[0173] In the optical recording/reproducing apparatus of FIG. 13, themulti-pulse drive current in which data is modulated is supplied to thesemiconductor laser, and the laser emits the laser beam to the disk. Asequence of data blocks, including marks and spaces, are recorded ontothe recording layer of the disk by focusing the laser beam on therecording layer of the disk.

[0174] Generally, when recording data onto the optical recording mediaby using the multi-pulse laser driving waveform, the opticalrecording/reproducing apparatus of the present embodiment is required tomaintain the accurate power levels of the laser optical output,including the peak power (Pw) corresponding to the peak- level drivecurrent, the bottom power (Pb) corresponding to the bottom-level drivecurrent, and the space power (Ps) corresponding to the space-level drivecurrent.

[0175] Alternatively, in the multi-pulse laser driving waveform, thebottom power (Pb) and the space power (Ps) may be consideredapproximately equal to each other. However, the space power of the laseroptical output must be detected, and it is necessary to set the spacepower at a relatively high level. Also, it is desired to set the bottompower as low as possible in order to achieve good jittercharacteristics. Hence, the optical recording/reproducing apparatus ofthe present embodiment is configured to maintain the three power levelsof the laser optical power, including the peak power (Pw), the bottompower (Pb), and the space power (Ps).

[0176] A description will now be provided of the automatic power control(APC) process, which is performed by the optical recording/reproducingapparatus of the present embodiment during a normal writing process.

[0177] As shown in FIG. 13, the optical recording/reproducing apparatusof the present embodiment generally comprises a central processing unit(CPU) 1, a laser diode (LD) 2, a photodetector (PD) 3, a laser diodedriver (LDD) 4, a current-voltage converter 5, a sample/hold circuit 6,an analog-to-digital converter (ADC) 7, a laser drive waveform controlunit (LDWC) 11, a bias current source (BCS) 12, a bottom-level currentdriver (BCD) 18, a space-level current source (SCS) 19, and a peak-levelcurrent source (PCS) 20.

[0178] In the optical recording/reproducing apparatus of FIG. 13, theCPU 1 sets a bottom-level increment current at the output of thebottom-level current driver (BCD) 18 by supplying a bottom-level control(BLC) signal to the BCD 18. The signal line through which the BLC signalis sent from the CPU 1 to the BCD 18 is designated by reference numeral204. The signal line through which the bottom-level increment current issent from the BCD 18 to the LDD 4 is designated by reference numeral208.

[0179] The CPU 1 sets a peak-level increment current at the output ofthe peak-level current source (PCS) 20 by supplying a peak-level control(PLC) signal to the PCS 20. The signal line through which the PLC signalis sent from the CPU 1 to the PCS 20 is designated by reference numeral207. The signal line through which the peak-level increment current issent from the PCS 20 to the LDD 4 is designated by reference numeral210.

[0180] The CPU 1 sets a space-level increment current at the output ofthe space-level current source (SCS) 19 by supplying a space-levelcontrol (SLC) signal to the SCS 19. The signal line through which theSLC signal is sent from the CPU 1 to the SCS 19 is designated byreference numeral 206. The signal line through which the space-levelincrement current is sent from the SCS 19 to the LDD 4 is designated byreference numeral 209.

[0181] The LDD 4 is required to supply a bias-level current, which isabove an oscillation threshold value of the laser light source, to thelaser diode (LD) 2. For this purpose, the CPU 1 sets a bias-level drivecurrent at the output of the bias current source (BCS) 12 by supplying abias-level control (BIASLC) signal to the BCS 12. The signal linethrough which the BIASLC signal is sent from the CPU 1 to the BCS 12 isdesignated by reference numeral 220. The signal line through which thebias-level drive current is sent from the BCS 12 to the LDD 4 isdesignated by reference numeral 221.

[0182] Specifically, each of the SCS 19 and the PCS 20 is configured byusing a digital-to-analog converter (DAC). The digital space-levelcontrol signal from the CPU 1 is received at the SCS 19, and, inresponse to the control signal, the SCS 19 outputs the analogspace-level increment current to the LDD 4. The digital peak-levelcontrol signal from the CPU 1 is received at the PCS 20, and, inresponse to the control signal, the PCS 20 outputs the analog peak-levelincrement current to the LDD 4.

[0183] The BCD 18 is configured so that the BCD 18 selectively outputsone of a plurality of bottom-level increment currents to the LDD 4through the signal line 208 in response to control signals supplied bythe CPU 1.

[0184] The LDD 4 receives the bias-level drive current from the signalline 221, the bottom-level increment current from the signal line 208,the space-level increment current from the signal line 209 and thepeak-level increment current from the signal line 210, and, in responseto the current signals, the LDD 4 supplies a selected one of the drivecurrents to the laser diode (LD) 2 at a time under the control of theCPU 1.

[0185] The laser drive waveform control (LDWC) unit 11 converts asequence of input recording data blocks into an eight-to-sixteenmodulation (ESM) signal as in the waveform indicated by (a) in FIG. 15.The LDWC unit 11 further generates a multi-pulse laser driving waveformas in the waveform indicated by (e) in FIG. 15. In accordance with themulti-pulse laser driving waveform, the LDWC unit 11 supplies abottom-power enable (BPE) signal 201, a space-power enable (SPE) signal202 and a peak-power enable (PPE) signal 203, to the LDD 4.

[0186] When the bottom-power enable (BPE) signal 201 is set in the highlevel (H), the LDD 4 supplies a sum of the bias-level drive current 221and the bottom-level increment current 208 to the LD 2. The LD 2 at thistime is driven to output the laser beam at the bottom power (Pb). Whenthe space-power enable (SPE) signal 202 is set in the high level (H),the LDD 4 supplies a sum of the bias-level drive current 221 and thespace-level increment current 209 to the LD 2. The LD 2 at this time isdriven to output the laser beam at the space power (Ps). When thepeak-power enable (PPE) signal 203 is set in the high level (H), the LDD4 supplies a sum of the bias-level drive current 221 and the peak-levelincrement current 210 to the LD 2. The LD 2 at this time is driven tooutput the laser beam at the peak power (Pw). See the waveforms of theoutput signals of the corresponding elements of the opticalrecording/reproducing apparatus of FIG. 13, which are shown by (a)through (e) in FIG. 15.

[0187] When the drive current is supplied from the LDD 4 to the LD 2,the LD 2 emits the laser beam to the optical recording medium, so thatthe data is recorded onto or reproduced from the recording layer of therecording medium. The laser beam emitted by the LD 2 is received at thephotodetector (PD) 3. The PD 3 outputs a monitoring current that isproportional to the laser optical power of the received laser beam. Themonitoring current is supplied from the PD 3 to the current-voltageconverter 5. The signal line through the monitoring current signal issent from the PD 3 to the current-voltage converter 5 is designated byreference numeral 112.

[0188] The current-voltage converter 5 outputs a power-monitoring signalbased on the monitoring current supplied by the PD 3. The signal linethrough the power monitoring signal is sent from the current-voltageconverter 5 to the sample/hold circuit 6 is designated by referencenumeral 113. By utilizing the power-monitoring signal 113 output by thecurrent-voltage converter 5, the automatic power control (APC) processis performed by the optical recording/reproducing apparatus of thepresent embodiment.

[0189] In the optical recording/reproducing apparatus of FIG. 13, theCPU 1 is connected to the sample/hold circuit 6 through a signal line211, and a space-power sample timing (SPST) signal is sent from the CPU1 to the sample/hold circuit 6 through the signal line 211. When a longspace having a maximum data length (in a case of the ESM scheme, 14T) isformed on the disk by the laser beam of the LD 2 during the normalrecording process, the CPU 1 sets the space-power sample timing (SPST)signal in the high level (H). When the SPST signal is set in the highlevel (H), the power-monitoring signal 113 is sampled and held by thesample/hold circuit 6. The ADC 7 converts the power-monitoring signal,held by the sample/hold circuit 6, into a digital space-power sample(SPS) signal. The SPS signal is supplied from the ADC 7 to the CPU 1through a signal line 214. See the waveforms indicated by (f) through(h) in FIG. 15.

[0190] The SPS signal output by the ADC 7 is received at the CPU 1, andthe CPU 1 compares the received SPS signal with a reference value. TheCPU 1 corrects the space-level control (SLC) signal 206, which issupplied to the space-level current source (SCS) 19, based on adifference between the SPS signal and the reference value. As thecorrected SLC signal 206 is supplied to the SCS 19, the SCS 19 suppliesa corrected space-level increment current to the LDD 4 so that the spacepower (Ps) of the laser optical output is maintained at a proper level.The LD 2 at this time is driven by the corrected space-level drivecurrent supplied by the LDD 4, so as to emit the laser beam at theproper space power (Ps).

[0191] Further, in the present embodiment, the CPU 1 calculates abottom-level drive current “Ib” and a peak-level drive current “Iw”based on the corrected space-level drive current and a derivativeefficiency, which will be described below.

[0192]FIG. 17 shows a laser diode derivative efficiency of the light vs.current characteristics of the laser diode used by the opticalrecording/reproducing apparatus of FIG. 13.

[0193] Hereinafter, the derivative efficiency “η” of the LD 2 used bythe optical recording/reproducing apparatus of the present embodiment,is defined as being a gradient ΔP/ΔI of the light vs. currentcharacteristic curve as shown in FIG. 17.

[0194] Suppose that the bias-level drive current corresponding to thebias power, the bottom-level drive current corresponding to the bottompower Pb, the space-level drive current corresponding to the space powerPs, and the peak-level drive current corresponding to the peak power Pware represented by “Ibias”, “Ib”, “Is”, and “Iw”, respectively. As isapparent from the light vs. current characteristic curve of FIG. 17, thebottom power “Pb” and the peak power “Pw” are represented by thefollowing equations.

Pb=Ps—η×(Is—Ib)   (11)

Pw=Ps+η×(Iw—Is)   (12)

[0195] From the above equations (11) and (12), the bottom-level drivecurrent “Ib” and the peak-level drive current “Iw” can be calculated inaccordance with the following equations.

Ib=Is—(Ps—Pb)/η  )13)

Iw=Is+(Pw—Ps)/η  (14)

[0196] In the case of the APC process, the derivative efficiency “η” ofthe LD 2 is predetermined, and the calculation of the bottom-level drivecurrent Ib and the peak-level drive current Iw is performed by using thepredetermined derivative efficiency. As described above, the CPU 1calculates the bottom-level drive current “Ib” and the peak-level drivecurrent “Iw” based on the corrected space-level drive current and thederivative efficiency. Thereafter the CPU 1 sets the bottom-levelcontrol signal 204 and the peak-level control signal 207, which arerespectively supplied to the bottom-level current driver 18 and thepeak-level current source 20, to the proper values based on thecalculated drive currents “Ib” and “Iw”.

[0197] As described above, the LDD 4 supplies the sum of the bias-leveldrive current 221 and the bottom-level increment current 208 to the LD2. Also, the LDD 4 supplies the sum of the bias-level drive current 221and the space-level increment current 209 to the LD 2. Further, the LDD4 supplies the sum of the bias-level drive current 221 and thepeak-level increment current 210 to the LD 2. Suppose that thebias-level drive current 221, the space-level increment current 209 andthe peak-level increment current 210 are represented by “ΔIb”, “ΔIs” and“ΔIw”, respectively. As is apparent from the characteristic curve shownin FIG. 17, the bottom-level drive current “Ib”, the space-level drivecurrent “Is” and the peak-level drive current “Iw” can be calculated inaccordance with the following equations.

Ib=I bias+ΔI b   (15)

Is=I bias+ΔI s   (16)

Iw=I bias+ΔIw   (17)

[0198] In the present embodiment, a time period for which theabove-described APC process is performed is shorter than a time periodfor which a special power setting process (which will be describedlater) is performed. For example, in the present embodiment, the spacepower sample (SPS) signal 214, output by the ADC 7, is received by theCPU 1 when a long space having a maximum data length (14T) is formed onthe disk by the laser beam of the LD 2. As described above, at thistime, the space-power sample timing (SPST) signal is set in the highlevel by the CPU 1.

[0199] According to the DVD standards, the data length 14T of a longspace is equal to the data length of a sync code in the sequence of theinput recording data blocks, and the sampling and holding of the spacepower in the APC process will be performed once for every two syncframes (1488T).

[0200] Strictly speaking, either a mark having the maximum data length14T or a space having the maximum data length 14T is selected so as tomeet the requirement that the digital sum value (DSV) be equal to zero.The sampling and holding of the space power in the APC process is notalways performed once for every two sync frames (1488T). However, forthe sake of simplicity, it is assumed that, in the present embodiment, amark having the data length 14T and a space having the data length 14Tare alternately selected with equal probabilities.

[0201] In the optical recording/reproducing apparatus of the presentembodiment, the CPU 1 calculates the bottom-level drive current “Ib” andthe peak-level drive current “Iw” based on the corrected space-leveldrive current (obtained when forming a long space having the maximumdata length 14T on the disk by the laser beam of the LD 2) and thepredetermined derivative efficiency. Accordingly, the opticalrecording/reproducing apparatus of the present embodiment is effectivein maintaining the accurate recording power levels of the laser opticalpower, including the peak 5 power, the space power and the bottom power,even when the light-receiving module with the limited bandwidth is used.

[0202]FIG. 18 shows the light vs. current characteristics of the laserdiode with a variation of the derivative efficiency during the writingmode.

[0203] As shown in FIG. 18, the light vs. current characteristic curvetends to shift and bend to the right with increasing temperature, andthe derivative efficiency of the laser diode tends to vary withincreasing temperature. If the derivative efficiency varies, the errorsof the calculated bottom-level drive current “Ib” and the calculatedpeak-level drive current “Iw” will not be negligible.

[0204] As previously described, the conventional apparatus, disclosed inJapanese Laid-Open Patent Application No.9-171631, carries out the powercontrol process in which the bottom-level drive current to the laserdiode is corrected by using the detected peak power and the detectedspace power, in order to take measures against a variation of thederivative efficiency. However, according to the above-mentioned powercontrol process, a problem arises in that the formation of a mark on therecording layer of the disk when the laser diode is driven at thepeak-level drive current in the non-pulse condition becomes deficient.

[0205] In order to eliminate the above problem of the conventionalapparatus, the optical recording/reproducing apparatus of the presentembodiment is configured so that the bottom-level current driver (BCD)18 selectively outputs one of the plurality of bottom-level incrementcurrents to the LDD 4 through the signal line 208 in response to thecontrol signals supplied by the CPU 1. A specific one (which is equal tothe peak-level increment current) among the plurality of bottom-levelincrement currents, which is supplied from the BCD 18 to the LDD 4during a special power setting process, results in the peak-level drivecurrent supplied to the LD 2 by the LDD 4. The peak power level of thelaser optical output when the specific bottom-level increment current issupplied to the LDD 4 by the BCD 18, is sampled and held by thesample/hold circuit 6, and the corresponding peak power sample (PPS)signal is received at the CPU 1. Then, the CPU 1 calculates a derivativeefficiency of the LD 2 based on the space power sample (SPS) obtainedduring the normal APC process and the peak power sample (PPS) obtainedduring the special power setting process.

[0206] Next, a description will be provided of the special power settingprocess executed by the optical recording/reproducing apparatus of thepresent embodiment with reference to FIG. 14 and FIG. 16.

[0207] As shown in FIG. 14, the bottom-level current driver (BCD) 18 inthe present embodiment generally comprises a first digital-to-analogconverter (DAC) 82, a second digital-to-analog converter (DAC) 83, and aswitch 84. The switch 84 has a high-level state and a low-level state.The bottom-level select (BLS) signal output by the CPU 1 is sent to theswitch 84 through the signal line 215, and one of the high-level (H)state and the low-level (L) state is selected at the switch 84 inaccordance with the bottom-level select (BLS) signal 215 supplied by theCPU 1.

[0208] The first DAC 82 has an input connected to the signal line 204and an output connected to the switch 84. When the high-level (H) stateof the switch 84 is selected according to the BLS signal 215, the BCD 18supplies an output signal of the first DAC 82 to the LDD 4 through thesignal line 208. The second DAC 83 has an input connected to the signalline 205 and an output connected to the switch 84. When the low-level(L) state of the switch 84 is selected according to the BLS signal 215,the BCD 18 supplies an output signal of the second DAC 83 to the LDD 4through the signal line 208.

[0209] The normal bottom-level control (BLC) signal, which is sentthrough the signal line 204 by the CPU 1 when producing the normalbottom power (Pb) of the laser optical output, is received at the firstDAC 82, and, in response to the normal BLC signal, the DAC 82 outputsthe normal bottom-level increment current (BIC) to the switch 84.Usually when the bottom power (Pb) of the laser optical output isproduced, the high-level (H) state of the switch 84 is selectedaccording to the BLS signal 215.

[0210] A second bottom-level control (BLC) signal, which is sent throughthe signal line 205 by the CPU 1 during the special power settingprocess, is received at the second DAC 83, and, in response to thesecond BLC signal, the DAC 83 outputs a second bottom-level incrementcurrent (BIC) that is equal to the peak-level increment current (PIC),to the switch 84.

[0211] In the present embodiment, the frequency at which the executionof the special power setting process is initiated by the CPU 1 issmaller than the frequency at which the execution of the normal APCprocess is initiated by the CPU 1. An optimal value of the frequency ofexecution of the special power setting process may be experimentallydetermined depending on time-dependent variations of the derivativeefficiency of the LD 2.

[0212] At a start of the special power setting process, the CPU 1 sendsa second BLC signal 205 to the second DAC 83, and the second DAC 83outputs a second BIC (equal to the PIC) to the switch 84. The low state(L) of the switch 84 is selected according to the BLS signal 215, andthe second BIC, supplied to the LDD 4 by the BCD 18, results in the peakpower (Pw) of the laser beam of the LD 2. See the state (2) indicated inFIG. 16.

[0213] In the above-described condition, when recording a 14T mark data“14TM” onto the disk, the CPU 1 sets the BLS signal 215 in the low state(L), and the DAC 83 supplies the second BIC to the LDD 4 through thesignal line 208. At the same time, the CPU 1 sets the SPST signal 211 inthe high state (H). Hence, only during the 14T period, the peak power“Pw” of the laser beam of the LD 2 is produced. In other words, duringthe special power setting process, the LD 2 is driven in the non-pulsecondition by the LDD 4 to emit the peak-power laser beam to the disk.

[0214] In the above-described condition, a corresponding peak powersample (PPS) signal 214, output by the ADC 7, is received by the CPU 1.The CPU 1 stores the received PPS signal in a portion of the memory thatis different from a memory portion in which the SPS signal obtainedduring the APC process is stored.

[0215] Immediately after the 14T mark data is recorded onto the disk,the CPU 1 sets the BLS signal 215 in the high state (H). The high state(H) of the switch 84 is selected according to the BLS signal 215 so asto produce the normal bottom power “Pb” of the laser beam of the LD 2.See the state (3) indicated in FIG. 16.

[0216] In the present embodiment, the 14T mark data, recorded onto thedisk during the special power setting, tends to become deficient.However, only the 14T period during the special power setting process,the peak-power laser beam of the LD 2 is driven in the non-pulsecondition. If the time interval between the special power setting cyclesis set to a relatively long time and the error correcting code functionis used when reproducing the data from the disk, the deterioration ofthe jitter characteristics will be negligible.

[0217] In the present embodiment, the CPU 1 calculates a derivativeefficiency “η” of the LD 2 based on the space power sample (SPS) signal(=Ps), obtained during the normal APC process, and the peak power sample(PPS) signal (=Pw), obtained during the special power setting process,and the corresponding drive currents (Is, I w), by using the followingequation.

η=(Pw—Ps)/(Iw—Is)   (18)

[0218] See the light vs. current characteristics shown in FIG. 17, foran example of the calculation of the derivative efficiency used by thepresent embodiment at this time.

[0219] If the setting of the second DAC 83 for the second bottom-poweroutput (equal to the peak power output) can be performed timely, thesecond bottom-power laser driving may be performed within a period the14T mark data is output.

[0220] In the above-described embodiment, the bottom-level currentdriver (BCD) 18 selectively outputs one of the plurality of bottom-levelincrement currents to the LDD 4 in response to the bottom-level selectsignal 215 and the bottom-level control signals 204 and 205, theplurality of bottom-level increment currents including the normalbottom-level increment current supplied to the LDD 4 during the normalAPC process and the second bottom-level increment current supplied tothe LDD 4 during the special power setting process, the secondbottom-level increment current supplied to the LDD 4 resulting in thepeak-level drive current to the LD 2.

[0221] Accordingly, the optical recording/reproducing apparatus of thepresent embodiment can provide accurate calculation of the derivativeefficiency with little calculation errors and prevent the deteriorationof the jitter characteristics and the deficiency of the mark formation.The optical recording/reproducing apparatus of the present embodiment iseffective in maintaining the accurate recording power levels of thelaser optical output, including the peak power, the space power and thebottom power, even when the light-receiving module with the limitedbandwidth is used.

[0222] Further, in the optical recording/reproducing apparatus of thepresent embodiment, the BCD 18 is configured so that the normalbottom-level increment current, supplied from the BCD 18 to the LDD 4,is changed to the second bottom-level increment current during theperiod a mark data having the maximum data length 14T is formed on thedisk. Therefore, the deterioration of the jitter characteristics whenreproducing the data from the disk will be negligible.

[0223] Next, a description will be provided of another preferredembodiment of the optical recording/reproducing apparatus of theinvention with reference to FIG. 19 through FIG. 21.

[0224]FIG. 19 shows the optical recording/reproducing apparatus of thepresent embodiment. FIG. 20 shows a space-level current driver in theoptical recording/reproducing apparatus of FIG. 19. FIG. 21 shows theexemplary waveforms of the output signals of the elements of the opticalrecording/reproducing apparatus of FIG. 19 during the normal writingmode and during the special power setting mode.

[0225] In the present embodiment, in the multi-pulse laser drivingwaveform, the bottom power (Pb) and the space power (Ps) is consideredapproximately equal to each other. In other words, the opticalrecording/reproducing apparatus of the present embodiment is configuredto maintain the two power levels of the laser optical power, includingthe peak power (Pw) and the space power (Ps).

[0226] A description will now be provided of the automatic power control(APC) process, which is performed by the optical recording/reproducingapparatus of the present embodiment during a normal writing process.

[0227] As shown in FIG. 19, the optical recording/reproducing apparatusof the present embodiment generally comprises a central processing unit(CPU) 1, a laser diode (LD) 2, a photodetector (PD) 3, a laser diodedriver (LDD) 34, a current-voltage converter 5, a sample/hold circuit 6,an analog-to-digital converter (ADC) 7, a laser drive waveform controlunit (LDWC) 31, a bias current source (BCS) 12, a space-level currentdriver (SCD) 39, and a peak-level current source (PCS) 30.

[0228] In the optical recording/reproducing apparatus of FIG. 19, theCPU 1 sets a peak-level increment current at the output of thepeak-level current source (PCS) 30 by supplying a peak-level control(PLC) signal to the PCS 30. The signal line through which the PLC signalis sent from the CPU 1 to the PCS 30 is designated by reference numeral307. The signal line through which the peak-level increment current issent from the PCS 30 to the LDD 34 is designated by reference numeral310.

[0229] The CPU 1 sets a normal space-level increment current at theoutput of the space-level current driver (SCD) 39 by supplying a firstspace-level control (SLC) signal to the SCD 39. The signal line throughwhich the first SLC signal is sent from the CPU 1 to the SCD 39 isdesignated by reference numeral 305. Further, the CPU 1 sets a secondspace-level increment current at the output of the SCD 39 by supplying asecond space-level control (SLC) signal to the SCD 39. The signal linethrough which the second SLC signal is sent from the CPU 1 to the SCD 39is designated by reference numeral 306. The signal line through whichone of the normal and second SIC currents is sent from the SCD 39 to theLDD 34 is designated by reference numeral 309.

[0230] The LDD 34 is required to supply a bias-level current, which isabove an oscillation threshold value of the laser light source, to thelaser diode (LD) 2. For this purpose, the CPU 1 sets a bias-level drivecurrent at the output of the bias current source (BCS) 12 by supplying abias-level control (BIASLC) signal to the BCS 12. The signal linethrough which the BIASLC signal is sent from the CPU 1 to the BCS 12 isdesignated by reference numeral 220. The signal line through which thebias-level drive current is sent from the BCS 12 to the LDD 34 isdesignated by reference numeral 221.

[0231] As described above, the SCD 39 is configured so that the SCD 39selectively outputs one of the normal and second space-level incrementcurrents (SIC) to the LDD 34 through the signal line 309 in response tocontrol signals supplied by the CPU 1.

[0232] The LDD 34 receives the bias-level drive current from the signalline 221, the space-level increment current from the signal line 309 andthe peak-level increment current from the signal line 310, and, inresponse to the current signals, the LDD 34 supplies a selected one ofthe drive currents to the laser diode (LD) 2 at a time under the controlof the CPU 1.

[0233] The laser drive waveform control (LDWC) unit 31 converts asequence of input recording data blocks into an eight-to-sixteenmodulation (ESM) signal as in the waveform indicated by (a) in FIG. 21.The LDWC unit 31 further generates a multi-pulse laser driving waveformas in the waveform indicated by (d) in FIG. 21. In accordance with themulti-pulse laser driving waveform, the LDWC unit 31 supplies aspace-power enable (SPE) signal 302 and a peak-power enable (PPE) signal303, to the LDD 34.

[0234] When the space-power enable (SPE) signal 302 is set in the highlevel (H), the LDD 34 supplies a sum of the bias-level drive current 221and the space-level increment current 309 to the LD 2. The LD 2 at thistime is driven to output the laser beam at the space power (Ps). Whenthe peak-power enable (PPE) signal 303 is set in the high level (H), theLDD 34 supplies a sum of the bias-level drive current 221 and thepeak-level increment current 310 to the LD 2. The LD 2 at this time isdriven to output the laser beam at the peak power (Pw). See thewaveforms of the output signals of the corresponding elements of theoptical recording/reproducing apparatus of FIG. 19, which are shown by(a) through (d) in FIG. 21.

[0235] When the drive current is supplied from the LDD 34 to the LD 2,the LD 2 emits the laser beam to the optical recording medium, so thatthe data is recorded onto or reproduced from the recording layer of therecording medium. The laser beam emitted by the LD 2 is received at thephotodetector (PD) 3. The PD 3 outputs a monitoring current that isproportional to the laser optical power of the received laser beam. Themonitoring current 112 is supplied from the PD 3 to the current-voltageconverter 5.

[0236] The current-voltage converter 5 outputs a power-monitoring signal113 to the sample/hold circuit 6 based on the monitoring current 112supplied by the PD 3. By utilizing the power-monitoring signal 113output by the current-voltage converter 5, the automatic power control(APC) process is performed by the optical recording/reproducingapparatus of the present embodiment.

[0237] In the optical recording/reproducing apparatus of FIG. 19, theCPU 1 is connected to the sample/hold circuit 6 through a signal line311, and a space-power sample timing (SPST) signal is sent from the CPU1 to the sample/hold circuit 6 through the signal line 311. When a longspace having a maximum data length (in a case of the ESM scheme, 14T) isformed on the disk by the laser beam of the LD 2 during the normalrecording process, the CPU 1 sets the space-power sample timing (SPST)signal in the high level (H). When the SPST signal is set in the highlevel (H), the power-monitoring signal 113 is sampled and held by thesample/hold circuit 6. The ADC 7 converts the power-monitoring signal,held by the sample/hold circuit 6, into a digital space-power sample(SPS) signal. The SPS signal is supplied from the ADC 7 to the CPU 1through a signal line 314. See the waveforms indicated by (e) through(g) in FIG. 21.

[0238] The SPS signal output by the ADC 7 is received at the CPU 1, andthe CPU 1 compares the received SPS signal with a reference value. TheCPU 1 corrects the space-level control (SLC) signal 305, which issupplied to the space-level current driver (SCD) 39, based on adifference between the SPS signal and the reference value. As thecorrected SLC signal 305 is supplied to the SCD 39, the SCD 39 suppliesa corrected space-level increment current to the LDD 34 so that thespace power (Ps) of the laser optical output is maintained at a properlevel. The LD 2 at this time is driven by the corrected space-leveldrive current supplied by the LDD 34, so as to emit the laser beam atthe proper space power (Ps).

[0239] Further, in the present embodiment, the CPU 1 calculates apeak-level drive current “Iw” based on the corrected space-level drivecurrent and the derivative efficiency of the laser diode by using theabove equation (12).

[0240] As previously described, the derivative efficiency “η” of the LD2 used by the optical recording/reproducing apparatus of the presentembodiment, is defined as being a gradient ΔP/ΔI of the light vs.current characteristic curve as shown in FIG. 17.

[0241] In the case of the APC process, the derivative efficiency “η” ofthe LD 2 is predetermined, and the calculation of the peak-level drivecurrent Iw is performed by using the predetermined derivativeefficiency. As described above, the CPU 1 calculates the peak-leveldrive current “Iw” based on the corrected space-level drive current andthe derivative efficiency. Thereafter the CPU 1 sets the peak-levelcontrol signal 307, which is supplied to the peak-level current source30, to the proper value based on the calculated drive current “Iw”.

[0242] As described above, the LDD 34 supplies the sum of the bias-leveldrive current 221 and the space-level increment current 309 to the LD 2.Further, the LDD 34 supplies the sum of the bias-level drive current 221and the peak-level increment current 310 to the LD 2. The space-leveldrive current “Is” and the peak-level drive current “Iw” can becalculated in accordance with the above equations (16) and (17).

[0243] In the present embodiment, a time period for which theabove-described APC process is performed is shorter than a time periodfor which a special power setting process (which will be describedlater) is performed. For example, in the present embodiment, the spacepower sample (SPS) signal 314, output by the ADC 7, is received by theCPU 1 when a long space having a maximum data length (14T) is formed onthe disk by the laser beam of the LD 2. As described above, at thistime, the space-power sample timing (SPST) signal is set in the highlevel by the CPU 1.

[0244] In the optical recording/reproducing apparatus of the presentembodiment, the CPU 1 calculates the peak-level drive current “Iw” basedon the corrected space-level drive current and the predeterminedderivative efficiency. Accordingly, the optical recording/reproducingapparatus of the present embodiment is effective in maintaining theaccurate recording power levels of the laser optical power, includingthe peak power and the space power, even when the light-receiving modulewith the limited bandwidth is used.

[0245] In the present embodiment, the SCD 39 is configured so that theSCD 39 selectively outputs one of the plurality of space-level incrementcurrents to the LDD 34 through the signal line 309 in response to thecontrol signals supplied by the CPU 1. A specific one (which is equal tothe peak-level increment current) among the plurality of space-levelincrement currents, which is supplied from the SCD 39 to the LDD 34during a special power setting process, results in the peak-level drivecurrent supplied to the LD 2 by the LDD 34. The peak power level of thelaser optical output when the specific space-level increment current issupplied to the LDD 34 by the CSD 39, is sampled and held by thesample/hold circuit 6, and the corresponding peak power sample (PPS)signal is received at the CPU 1. Then, the CPU 1 calculates a derivativeefficiency of the LD 2 based on the space power sample (SPS) obtainedduring the normal APC process and the peak power sample (PPS) obtainedduring the special power setting process.

[0246] Next, a description will be provided of the special power settingprocess executed by the optical recording/reproducing apparatus of thepresent embodiment with reference to FIG. 20 and FIG. 21.

[0247] As shown in FIG. 20, the space-level current driver (SCD) 39 inthe present embodiment generally comprises a first digital-to-analogconverter (DAC) 392, a second digital-to-analog converter (DAC) 393, anda switch 394. The switch 394 has a high-level state and a low-levelstate. The space-level select (SLS) signal output by the CPU 1 is sentto the switch 394 through the signal line 315, and one of the high-level(H) state and the low-level (L) state is selected at the switch 394 inaccordance with the SLS signal 315 supplied by the CPU 1.

[0248] The first DAC 392 has an input connected to the signal line 305and an output connected to the switch 394. When the high-level (H) stateof the switch 394 is selected according to the SLS signal 315, the SCD39 supplies an output signal of the first DAC 392 to the LDD 34 throughthe signal line 309. The second DAC 393 has an input connected to thesignal line 306 and an output connected to the switch 394. When thelow-level (L) state of the switch 394 is selected according to the SLSsignal 315, the SCD 39 supplies an output signal of the second DAC 393to the LDD 34 through the signal line 309.

[0249] The normal space-level control (SLC) signal, which is sentthrough the signal line 305 by the CPU 1 when producing the normal spacepower (Ps) of the laser optical output, is received at the first DAC392, and, in response to the normal SLC signal, the DAC 392 outputs thenormal space-level increment current (SIC) to the switch 39. Usuallywhen the space power (Ps) of the laser optical output is produced, thehigh-level (H) state of the switch 394 is selected according to the SLSsignal 315.

[0250] A second space-level control (SLC) signal, which is sent throughthe signal line 306 by the CPU 1 during the special power settingprocess, is received at the second DAC 393, and, in response to thesecond SLC signal, the DAC 393 outputs a second space-level incrementcurrent (SIC) that is equal to the peak-level increment current (PIC),to the switch 394.

[0251] In the present embodiment, the frequency at which the executionof the special power setting process is initiated by the CPU 1 issmaller than the frequency at which the execution of the normal APCprocess is initiated by the CPU 1. An optimal value of the frequency ofexecution of the special power setting process may be experimentallydetermined depending on time-dependent variations of the derivativeefficiency of the LD 2.

[0252] At a start of the special power setting process, the CPU 1 sendsa second SLC signal 306 to the second DAC 393, and the second DAC 393outputs a second SIC (that is equal to the PIC) to the switch 394. Thelow state (L) of the switch 394 is selected according to the SLS signal315, and the second SIC, supplied to the LDD 34 by the SCD 39, resultsin the peak power (Pw) of the laser beam of the LD 2.

[0253] In the above-described condition, when recording a long mark datahaving the maximum data length 14T onto the disk, the CPU 1 sets the SLSsignal 315 in the low state (L), and the DAC 393 supplies the second SICto the LDD 34 through the signal line 309. At the same time, the CPU 1sets the SPST signal 311 in the high state (H). Hence, only during the14T period, the peak power “Pw” of the laser beam of the LD 2 isproduced. In other words, during the special power setting process, theLD 2 is driven in the non-pulse condition by the LDD 34 to emit thepeak-power laser beam to the disk.

[0254] In the above-described condition, a corresponding peak powersample (PPS) signal 314, output by the ADC 7, is received by the CPU 1.The CPU 1 stores the received PPS signal in a portion of the memory thatis different from a memory portion which stores the SPS signal obtainedduring the APC process.

[0255] Immediately after the 14T mark data is recorded onto the disk,the CPU 1 sets the SLS signal 315 in the high state (H). The high state(H) of the switch 394 is selected according to the SLS signal 315 so asto produce the normal space power “Ps” of the laser beam of the LD 2.

[0256] In the present embodiment, the CPU 1 calculates a derivativeefficiency “η” of the LD 2 based on the space power sample (SPS) signal(=Ps), obtained during the normal APC process, and the peak power sample(PPS) signal (=Pw), obtained during the special power setting process,and the corresponding drive currents (Is, I w), by using the aboveequation (18).

[0257] If the setting of the second DAC 393 for the second space-poweroutput (equal to the peak power output) can be performed timely, thesecond space-power laser driving may be performed within a period the14T mark data is output.

[0258] In the above-described embodiment, the space-level current driver(SCD) 39 selectively outputs one of the plurality of space-levelincrement currents to the LDD 34 in response to the space-level select(SLS) signal 315 and the space-level control signals 305 and 306, theplurality of space-level increment currents including the normalspace-level increment current supplied to the LDD 34 during the normalAPC process and the second space-level increment current supplied to theLDD 34 during the special power setting process, the second space-levelincrement current, supplied to the LDD 34, resulting in the peak-leveldrive current to the LD 2.

[0259] Accordingly, the optical recording/reproducing apparatus of thepresent embodiment can provide accurate calculation of the derivativeefficiency with little calculation errors and prevent the deteriorationof the jitter characteristics and the deficiency of the mark formation.The optical recording/reproducing apparatus of the present embodiment iseffective in maintaining the accurate recording power levels of thelaser optical output, including the peak power and the space power evenwhen the light-receiving module with the limited bandwidth is used.

[0260] Further, in the optical recording/reproducing apparatus of thepresent embodiment, the SCD 39 is configured so that the normalspace-level increment current (the normal SIC), supplied from the SCD 39to the LDD 34, is changed to the second space-level increment current(the second SIC) during the period a mark data having the maximum datalength 14T is formed on the disk. Therefore, the deterioration of thejitter characteristics when reproducing the data from the disk will benegligible.

[0261] Next, a description will now be provided of the basic concept ofthe optical recording/reproducing apparatus of the invention withreference to FIG. 19 and FIG. 12B.

[0262]FIG. 12B shows the basic concept of the opticalrecording/reproducing apparatus of the invention when a sequence ofrecording data blocks is recorded onto write-once read-many opticalrecording media (for example, a CD-R disk). For example, theconfiguration of the optical recording/reproducing apparatus shown inFIG. 19 is used to achieve the basic concept of the invention shown inFIG. 12B.

[0263] As indicated by (c) in FIG. 12B, the semiconductor laser driver(or the LDD 34) of the optical reproducing/reproducing apparatussupplies a selected one of a plurality of drive currents, including afirst-level drive current and a second-level drive current, to thesemiconductor laser (or the LD 2) to control the emission of a laserbeam by the laser.

[0264] The current driver (or the SCD 39) of the opticalrecording/reproducing apparatus selectively outputs one of a pluralityof increment currents to the laser driver in response to controlsignals, the plurality of increment currents including a first incrementcurrent supplied to the laser driver during the automatic power control(APC) process and a second increment current supplied to the laserdriver during the special power setting process.

[0265] The detection unit (or the elements 3, 5, 6 and 7 in FIG. 19)detects a first power sample signal (or the BPS signal 314), at a firstsampling point (indicated by “A” in FIG. 12B) of the waveform, from thelaser beam emitted when the first increment current (or the normal SIC)is supplied to the laser driver. The detection unit detects a secondpower sample signal (or the PPS signal 314), at a second sampling point(indicated by “B” in FIG. 12B) of the waveform, from the laser beamemitted when the second increment current (or the second SIC) issupplied to the laser driver.

[0266] The calculation unit (or the CPU 1) calculates a derivativeefficiency of the laser based on the first and second power samplesignals (the BPS and PPS signals 314) detected by the detection unit, sothat the drive currents of the laser driver, supplied to the laser, arecontrolled based on the calculated derivative efficiency.

[0267] Next, FIG. 22 shows another preferred embodiment of the opticalrecording/reproducing apparatus of the invention.

[0268]FIG. 23 shows a bias-level current driver in the opticalrecording/reproducing apparatus of FIG. 22. FIG. 24 is a time chart forexplaining exemplary waveforms of the output signals of the CPU of theoptical recording/reproducing apparatus of FIG. 22. FIG. 25 is a diagramfor explaining a relationship between the laser drive current and thelaser optical power.

[0269] In the optical recording/reproducing apparatus of the presentembodiment, the DVD-format code data is recorded onto a DVD-rewritabledisk (or a phase-change recording medium) by focusing a laser beamemitted by a laser diode, on the recording layer of the disk. Therecorded data is reproduced from the disk by the opticalrecording/reproducing apparatus. The optical recording/reproducingapparatus of the present embodiment employs the eight-to-sixteenmodulation (ESM) scheme as the data modulation method in order to carryout the pulse-width modulation (PWM) recording process for theDVD-rewritable disk.

[0270] In the optical recording/reproducing apparatus of FIG. 22, themulti-pulse drive current in which data is modulated is supplied to thelaser light source, and the laser light source emits the laser beam tothe DVD-rewritable disk. A stream of data blocks, including marks andspaces, are recorded onto the recording layer of the disk by focusingthe laser beam on the recording layer of the disk.

[0271] Generally, when recording data onto the phase-change recordingmedia by using the multi-pulse laser driving, the opticalrecording/reproducing apparatus is required to maintain the accuratepower levels of the laser optical power, including the peak power (Pw)corresponding to the peak-level drive current, the bias power (Pb)corresponding to the bias-level drive current, and the erase power (Pe)or space power corresponding to the erase-level drive current orspace-level drive current.

[0272] A description will now be provided of the automatic power control(APC) process which is performed by the optical recording/reproducingapparatus of the present embodiment.

[0273] As shown in FIG. 22, the optical recording/reproducing apparatusof the present embodiment generally comprises a central processing unit(CPU) 1, a laser diode (LD) 2, a photodetector (PD) 3, a laser diodedriver (LDD) 4, a current-voltage converter 5, a bias-level currentdriver (BCD) 47, an erase-level current driver (ECD) 48, and apeak-level current driver (PCD) 49. A digital-to-analog (D/A) converter41 and a digital-to-analog (D/A) converter 42 are provided between theCPU 1 and the BCD 47.

[0274] In the optical recording/reproducing apparatus of FIG. 22, theCPU 1 sets a peak-level increment current 407 at the output of thepeak-level current driver (PCD) 49 by supplying a peak-level control(PLC) signal 405 to the PCD 49. The CPU 1 sets an erase-level incrementcurrent 406 at the output of the erase-level current driver (ECD) 48 bysupplying an erase-level control (ELC) signal 404 to the ECD 48. The CPU1 sets a bias-level drive current 408 at the output of the bias-levelcurrent driver (BCD) 47 by supplying a target power signal (TPS) 412 tothe BCD 47 via the D/A converter 42.

[0275] Specifically, each of the ECD 48 and the PCD 49 is configured byusing a digital-to-analog converter (DAC). The digital erase- levelcontrol signal from the CPU 1 is received at the ECD 48, and, inresponse to the control signal, the ECD 48 outputs the analogerase-level increment current 406 to the LDD 4. The digital peak-levelcontrol signal from the CPU 1 is received at the PCD 49, and, inresponse to the control signal, the PCD 49 outputs the analog peak-levelincrement current 407 to the LDD 4.

[0276] The BCD 47 is configured so that the BCD 47 selectively outputsone of a plurality of bias-level drive current signals to the LDD 4through the signal line 408 in response to control signals supplied bythe CPU 1. Specifically, the BCD 47 is constructed as shown in FIG. 23,and outputs the bias-level drive current 408 to the LDD 4.

[0277] The LDD 4 receives the bias-level drive current 408, theerase-level increment current 406 and the peak-level increment current407, and determines the bias power Pb, the erase power Pe and the peakpower Pw of the laser diode 2. In response to the control signals fromthe CPU 1, the LDD 4 supplies a selected one of the drive currents tothe laser diode 2 at a controlled time.

[0278] In the optical recording/reproducing apparatus, the CPU 1converts a sequence of input recording data blocks into aneight-to-sixteen modulation (ESM) signal as in the waveform indicated by(a) in FIG. 24. The CPU 1 further generates a multi-pulse laser drivingwaveform as in the drive waveform indicated by (d) in FIG. 24. Inaccordance with the multi-pulse laser driving waveform, the CPU 1supplies an erase-power enable (EPE) signal 401 and a peak-power enable(PPE) signal 402 to the LDD 4 as indicated by (b) and (c) in FIG. 24.

[0279] When the erase-power enable (EPE) signal 401 is set in the highlevel (H), the LDD 4 supplies a sum of the bias-level drive current 408and the erase-level increment current 406 to the LD 2. The LD 2 isdriven by such erase-level drive current to output the laser beam at theerase power (Pe). When the peak-power enable (PPE) signal 402 is set inthe high level (H), the LDD 4 supplies a sum of the bias-level drivecurrent 408 and the peak-level increment current 407 to the LD 2. The LD2 is driven by such peak-level drive current to output the laser beam atthe erase power (Pw).

[0280] When the drive current is supplied from the LDD 4 to the LD 2,the LD 2 outputs the laser beam onto the phase-change recording medium,so that the data is recorded onto or reproduced from the recording layerof the phase-change recording medium. The laser beam output by the LD 2is received at the photodetector (PD) 3. The PD 3 outputs a monitorcurrent that is proportional to the laser optical power of the receivedlaser beam. The monitor current is supplied from the PD 3 to thecurrent-voltage converter 5 via a signal line 409. The current-voltageconverter 5 outputs a power-monitor signal (PMS) 410 based on themonitor current 409 supplied by the PD 3. The power monitor signal 410is supplied from the current-voltage converter 5 to sample-hold circuits702 and 704 of the BCD 47. By utilizing the power-monitor signal (PMS)410 supplied by the current-voltage converter 5, the BCD 47 performs theautomatic power control (APC) process in the opticalrecording/reproducing apparatus of the present embodiment.

[0281] As shown in FIG. 23, in the BCD 47 of the present embodiment, thepower monitor signal 410 from the current-voltage converter 5 issupplied to each of two amplifiers 701 and 703. The power monitor signal410 is amplified at each of the amplifiers 701 and 703, and suchamplified signals are supplied to the sample-hold circuits 702 and 704.The amplified power monitor signal is sampled and held by each of thesample-hold circuits 702 and 704.

[0282] The amplifier 701 and the sample-hold circuit 702 are used whenrecording information onto the dye recording layer of an opticalrecording medium. The amplifier 703 and the sample-hold circuit 704 areused when recording information onto the phase-change recording layer ofa phase-change recording medium.

[0283] In the bias-level current driver 47 of FIG. 23, the switch 709outputs a selected one of the output signals of the sample-hold circuits702 and 704 in response to the medium select signal 416 supplied by theCPU 1. The condition of the bias-level current driver 47 in which theAPC/ACC output compare signal 414 is set at the high level (H) is shownin FIG. 23.

[0284] The optical recording/reproducing apparatus of the presentembodiment is configured such that, when the data is recorded onto thephase-change recording medium, the erase-level drive current is sampledand held by the sample-hold circuit. However, the opticalrecording/reproducing apparatus of an alternative embodiment (which willbe described later) is configured such that, when the data is recordedonto the dye recording medium, the bias-level drive current is sampledand held by the sample-hold circuit. In order to make the levels of thesignals supplied from the sample-hold circuits 702 and 704 to an APCcircuit 705 nearly equal, regardless of the type of the recording media,the gain of the amplifier 701 is set at a value larger than a value ofthe gain of the amplifier 703.

[0285] The CPU 1 outputs the erase-power sampling signal 413 to the BCD47. When recording a long-space data (which is a space data with a datalength of lOT or more) on the recording medium, the sample-hold circuit704 samples and holds the power monitor signal 410 at the time thesampling signal 413 output by the CPU 1 changes from the high level (H)to the low level (L), and supplies the sampled signal to the APC circuit705. At this time, the switch 710 and the switch 712 are set to thehigh-level (H) condition as indicated in FIG. 23.

[0286] The CPU 1 outputs the target power signal 412 to the BCD 47through the D/A converter 42. The analog target power signal 412 outputby the D/A converter 42 is supplied to the inverting amplifier 708. Thetarget power signal is inverted at the amplifier 708 based on thereference voltage Vref. The sum of the inverted target power signaloutput from the amplifier 708 and the signal output from the sample-holdcircuit 704 is supplied to the inverting input of the APC circuit 705.

[0287] The APC circuit 705 in the present embodiment is configured byusing an integrator circuit. The output signal of the APC circuit 705 issupplied as the bias-level drive current 408 to the LDD 4 via the switch711. In this manner, the APC output feedback loop is formed in thepresent embodiment.

[0288] The APC circuit 705 controls the bias-level drive current 408such that the sum of the inverted target power signal output from theamplifier 708 and the signal output from the sample-hold circuit 704corresponds to the reference voltage Vref. In other words, the APCcircuit 705 controls the bias-level drive current 408 such that theoutput signal of the sample-hold circuit 704 is equal to the targetpower signal 112 output by the CPU 1.

[0289] In the BCD 47 shown in FIG. 23, the A/D converter 713 convertsthe analog bias-level drive current 408 into a digital signal, andoutputs the digital bias-level drive current signal 415 to the CPU 1. Inthis manner, when outputting a long space data, the opticalrecording/reproducing apparatus of the present embodiment controls thebias-level drive current 408 by sampling and holding the bias-leveldrive current signal (or the long space data).

[0290] In the present embodiment, the CPU 1 determines the erase-levelincrement current 406 and the peak-level increment current 407 based onthe digital bias-level drive current signal 415 supplied by the BCD 47.The bias-level drive current is controlled in response to the changes ofthe erase-level drive current, and the erase-level drive current isalways controlled by means of the analog power control.

[0291]FIG. 25 shows a laser diode derivative efficiency used by theoptical recording/reproducing apparatus of the present embodiment. Thederivative efficiency “η” of the LD 2 used by the opticalrecording/reproducing apparatus of the present embodiment, is defined asbeing a gradient ΔP/ΔI of the optical power vs. drive currentcharacteristic curve shown in FIG. 25.

[0292] Suppose that the bias-level drive current corresponding to thebias power Pb, the erase-level drive current corresponding to the erasepower Pe, and the peak-level drive current corresponding to the peakpower Pw are represented by “Ib”, “Ie”, and “Iw”, respectively. As isapparent from the optical power vs. drive current characteristic curveof FIG. 25, the erase-level increment current “ΔIe” and the peak-levelincrement current “ΔIw” are represented by the following equations.

ΔIe=(Pe—Pb)/η  (A)

ΔIw=(Pw—Pb)/η  (B)

[0293] The erase-level increment current “ΔIe” and the peak-levelincrement current “ΔIw” can be calculated in accordance with the aboveequations (A) and (B). In this case, the derivative efficiency “η” ofthe LD 2 is predetermined, and the calculations of the erase-levelincrement current “ΔIe” and the peak-level increment current “ΔIw” areperformed by using the predetermined derivative efficiency. As describedabove, the CPU 1 calculates the erase-level drive current “Ie” and thepeak-level drive current “Iw” based on the corrected erase-level drivecurrent and the derivative efficiency.

[0294] Next, a description will be given of operations of the opticalrecording/reproducing apparatus of the present embodiment when the CPU 1does not output the sampling signal 413 to the BCD 47 over a long periodexceeding a predetermined time.

[0295] If the sampling signal 413 is not output over a long periodexceeding a predetermined time, the output of the sample-hold circuit704 is gradually lowered due to the drooping characteristic. As the APCcircuit 705 controls the bias-level drive current 408 based on theoutput of the sample-hold circuit 704, irregularities of the laseroptical power are likely to occur.

[0296] In order to eliminate the problem, in the present embodiment, thelaser diode drive control of the CPU 1 is temporarily changed to anautomatic current control (ACC) process.

[0297] During the ACC process, the CPU 1 sets the bias-level drivecurrent 408 at the output of the BCD 47 by supplying an ACC drivecurrent (ADC) signal 411 to the BCD 47 via the D/A converter 41. In theBCD 47, the ADC signal 411 passes through the switch 711 (which is setto the low-level (L) condition), and is supplied to the LDD 4 as thebias-level drive current 408.

[0298] The sampling signal 413 is output to the monostable multivibrator714 as a trigger. At the rising edge of the sampling signal 413, themultivibrator 714 is set to the high-level (H) state. When the triggeris output within the predetermined time (e.g., 150 μs), themultivibrator 714 is set to the high-level (H) state. Otherwise themultivibrator 714 is set to the low-level (L) state.

[0299] When the output of the multivibrator 714 is set the low level(L), the laser diode drive control of the CPU 1 is changed to the ACCprocess. The multivibrator 714 outputs the ACC select signal (ACCSS) 750to each of the switch 710, the switch 711 and the switch 712. When thehigh-level ACCSS 750 from the multivibrator 714 is received, each of theswitches 710, 711 and 712 is set to the high-level (H) condition asshown in FIG. 23.

[0300]FIG. 26 is a time chart for explaining operations of thebias-level current driver (BCD) 47 of the present embodiment during theACC process.

[0301] When the switch 711 is set to the low-level (L) condition, theCPU 1 sets the bias-level drive current 408 at the output of the BCD 47by supplying the ADC signal 411 to the BCD 47. If, in this condition, along space data having a data length of 10T or more is produced, thenthe CPU 1 outputs the sampling signal 413 to the BCD 47. The output ofthe monostable multivibrator 714 is set to the high level (H), and thecontrol of the CPU 1 is quickly returned to the APC process.

[0302] When the switches 710 and 712 are set to the low-level (L)condition, the APC output feedback circuit 706 supplies the differencesignal between the output signal of the APC circuit 705 and the APCdrive current (ADC) signal 411, to the APC circuit 705. The APC circuit705 controls the bias-level drive current 408 such that the output ofthe APC output feedback circuit 706 corresponds to the reference voltageVref.

[0303] According to the present embodiment, it is possible to preventthe saturation of the output of the APC circuit 705 during the ACCprocess, and the setting of the bias-level drive current 108 can bequickly performed when the control of the CPU 1 is returned to the APCprocess.

[0304] In the BCD 47 shown in FIG. 23, the comparator 707 compares theoutput signal of the APC circuit 705 and the ACC drive current (ADC)signal 411, and supplies the difference signal thereof to the CPU 1 asthe APC/ACC output compare signal 414. By receiving the APC/ACC outputcompare signal 414, the CPU 1 sets the APC/ACC output compare signal 414such that the ADC signal 411 and the APC/ACC output compare signal 414are equal to each other.

[0305] In the optical recording/reproducing apparatus of the presentembodiment, even when the control of the CPU 1 is changed from the APCprocess to the ACC process, the bias-level drive current 408, which isnearly equal to the signal output by the APC circuit 705 immediatelybefore the change, is supplied to the LDD 4.

[0306] The optical recording/reproducing apparatus of the presentembodiment is effective in maintaining the accurate recording powerlevels of the laser diode optical power even when the sampling signal isnot output over a long period exceeding a predetermined time.

[0307] Next, FIG. 27 is a time chart for explaining exemplary waveformsof the output signals of the CPU of an alternative embodiment of theoptical recording/reproducing apparatus of FIG. 22.

[0308] The optical recording/reproducing apparatus of the presentembodiment has a configuration that is essentially the same as theconfiguration of the optical recording/reproducing apparatus of FIG. 22.Apart from the recording onto the phase-change recording medium as inthe previous embodiment, in the optical recording/reproducing apparatusof the present embodiment, the format code data is recorded onto adifferent type optical recording medium having a dye recording layer byfocusing a laser beam emitted by a laser diode, on the dye recordinglayer of the recording medium (which will be called the dye medium).

[0309] In the present embodiment, the recording power levels of thelaser diode optical power are two levels including the bias-power (Pb)level and the peak-power (Pw) level, and the bias-power level is sampledand held by the sample/hold circuit of the bias-level current driver(BCD) 47. Hence, as indicated by (b) in FIG. 27, the erase power enable(EPE) signal 401, which is output by the CPU 1 to the LDD 4, is alwaysset to the low level (L).

[0310] In the present embodiment, the medium select signal 416, which isoutput by the CPU 1 to the BCD 47, is set to the low level (L) so thatthe switch 709 is set to the low-level (L) condition. The power monitorsignal 410, which is output by the current-voltage converter 5 to theBCD 47, is amplified by the amplifier 701. The amplified power monitorsignal 410 is sampled and held by the sample/hold circuit 702, and theresulting signal is supplied to the APC circuit 705 via the switches 709and 710.

[0311] Similar to FIG. 24, in the present embodiment shown in FIG. 27,when the CPU 1 does not output the sampling signal 413 to the BCD 47over a long period exceeding a predetermined time (e.g., 150 μs), theoutput of the sample-hold circuit 704 is gradually lowered due to thedrooping characteristic. As the APC circuit 705 controls the bias-leveldrive current 408 based on the output of the sample-hold circuit 704,irregularities of the laser optical power are likely to occur.

[0312] In order to eliminate the problem, in the present embodiment, thelaser diode drive control of the CPU 1 is temporarily changed to theautomatic current control (ACC) process.

[0313] During the ACC process, the CPU 1 sets the bias-level drivecurrent 408 at the output of the BCD 47 by supplying the ACC drivecurrent (ADC) signal 411 to the BCD 47 via the DIA converter 41. In theBCD 47, the ADC signal 411 passes through the switch 711 (which is setto the low-level (L) condition), and is supplied to the LDD 4 as thebias-level drive current 408.

[0314] The sampling signal 413 is output to the monostable multivibrator714 as a trigger. At the rising edge of the sampling signal 413, themultivibrator 714 is set to the high-level (H) state. When the triggeris output within the predetermined time (e.g., 150 μs), themultivibrator 714 is set to the high-level (H) state. Otherwise themultivibrator 714 is set to the low-level (L) state.

[0315] When the output of the multivibrator 714 is set to the low level(L), the laser diode drive control of the CPU 1 is changed to the ACCprocess. The multivibrator 714 at this time outputs the low-level (L)ACC select signal (ACCSS) 750 to each of the switch 710, the switch 711and the switch 712, and each of the switches 710 to 712 is set to thelow-level (L) condition (not shown in FIG. 23). On the other hand, whenthe high-level ACCSS 750 from the multivibrator 714 is received at eachof the switches 710 to 712, each of the switches 710 to 712 is set tothe high-level (H) condition as shown in FIG. 23.

[0316] When the switch 711 is set to the low-level (L) condition, theCPU 1 sets the bias-level drive current 408 at the output of the BCD 47by supplying the ADC signal 411 to the BCD 47. If, in this condition, along space data having a data length of 10T or more is produced, thenthe CPU 1 outputs the sampling signal 413 to the BCD 47. The output ofthe monostable multivibrator 714 is set to the high level (H), and thecontrol of the CPU 1 is quickly returned to the APC process.

[0317] When the switches 710 and 712 are set to the low-level (L)condition, the APC output feedback circuit 706 supplies the differencesignal between the output signal of the APC circuit 705 and the APCdrive current (ADC) signal 411, to the APC circuit 705. The APC circuit705 controls the bias-level drive current 408 such that the output ofthe APC output feedback circuit 706 corresponds to the reference voltageVref.

[0318] According to the present embodiment, it is possible to preventthe saturation of the output of the APC circuit 705 during the ACCprocess, and the setting of the bias-level drive current 108 can bequickly performed when the control of the CPU 1 is returned to the APCprocess.

[0319] In the BCD 47, the comparator 707 compares the output signal ofthe APC circuit 705 and the ACC drive current (ADC) signal 411, andsupplies the difference signal thereof to the CPU 1 as the APC/ACCoutput compare signal 414. By receiving the APC/ACC output comparesignal 414, the CPU 1 sets the APC/ACC output compare signal 414 suchthat the ADC signal 411 and the APC/ACC output compare signal 414 areequal to each other.

[0320] In the optical recording/reproducing apparatus of the presentembodiment, even when the control of the CPU 1 is changed from the APCprocess to the ACC process, the bias-level drive current 408, which isnearly equal to the signal output by the APC circuit 705 immediatelybefore the change, is supplied to the LDD 4.

[0321] The optical recording/reproducing apparatus of the presentembodiment is effective in maintaining the accurate recording powerlevels of the laser diode optical power even when the sampling signal isnot output over a long period exceeding a predetermined time.

[0322] Next, FIG. 28 is a time chart for explaining exemplary waveformsof the output signals of another alternative embodiment of the opticalrecording/reproducing apparatus of FIG. 22. FIG. 29 is a block diagramof a counter in the optical recording/reproducing apparatus of theembodiment of FIG. 28.

[0323] The optical recording/reproducing apparatus of the presentembodiment has a configuration that is essentially the same as theconfiguration of the optical recording/reproducing apparatus of FIG. 22.In the optical recording/reproducing apparatus of the presentembodiment, the format code data is recorded onto the dye recordingmedium.

[0324] The monostable multivibrator 714 as in the previous embodimentgenerates the timing signal to change the control of the CPU 1 from theAPC process to the ACC process. As shown in FIG. 29, the multivibrator714 is replaced with the counter unit 714 in the present embodiment, andthe counter unit 714 includes a clock 714 a and a counter 714 b. Theclock 714 a outputs a clock signal at a relatively low frequency (e.g.,1 MHz), and this clock signal is supplied to one of two inputs of thecounter 714 b. The sampling signal 413 output by the CPU 1 is suppliedto the other input of the counter 714 b. The counter 714 b counts theclock signals output by the clock 714 a, and, when the number of theclock signals counted by the counter 714 b exceeds a predetermined value(e.g., 150 counts corresponding to 150 μs), the counter 714 b outputs alow-level (L) signal as the ACC select signal (ACCSS) 750 to each of theswitch 710, the switch 711 and the switch 712. Each of the switches 710to 712 is set to the low-level (L) condition (that is, the start of theACC process). On the other hand, when the sampling signal 413 isreceived at the counter 714 b, the counter 714 b is reset by the risingedge of the sampling signal 413 to output the high-level (H) signal toeach of the switches 710 to 712. Each of the switches 710 to 712 is setto the high-level (H) condition (that is, the restart of the APCprocess).

[0325] As shown in FIG. 28, when the CPU 1 outputs the sampling signal413 to the BCD 47 within the predetermined time (e.g., 150 μs), thecounter 714 b continues to output the high-level (H) ACCSS 750 to eachof the switches 710 to 712. The APC process is continuously performed.On the other hand, when the CPU 1 does not output the sampling signal413 to the BCD 47 over a long period exceeding the predetermined time(e.g., 150 μs), the counter 714 b outputs the low-level (L) ACCSS 750 toeach of the switches 710 to 712. The control of the CPU 1 is changedfrom the APC process to the ACC process. Then, the CPU 1 outputs thesampling signal 413 to the counter unit 417 of the BCD 47, and thecounter 714 b is reset by the rising edge of the sampling signal 413 tooutput the high-level (H) signal to each of the switches 710 to 712.Thus, the ACC process is terminated by the sampling signal 413, and theAPC process can quickly be restarted.

[0326] In the above-described embodiment, the counter unit 714,including the clock 714 a and the counter 714 b, is used to generate thetiming signal to change the control of the CPU 1 from the APC process tothe ACC process. Alternatively, a frequency-divided clock signal whichis generated by dividing the frequency of the channel clock may be usedinstead of the clock signal generated by the clock 714 a.

[0327] The optical recording/reproducing apparatus of the presentembodiment is effective in maintaining the accurate recording powerlevels of the laser diode optical power even when the sampling signal isnot output over a long period exceeding a predetermined time.

[0328] Next, FIG. 30 is a block diagram of another preferred embodimentof the optical recording/reproducing apparatus of the invention.

[0329]FIG. 31 shows a bias-level current driver in the opticalrecording/reproducing apparatus of FIG. 30. FIG. 32 shows an erase-levelcurrent driver in the optical recording/reproducing apparatus of FIG.30. FIG. 33 shows a multi-pulse laser drive waveform of the opticalrecording/reproducing apparatus of FIG. 30. FIG. 34 is a time chart forexplaining exemplary waveforms of the output signals of the CPU of theoptical recording/reproducing apparatus of FIG. 30.

[0330] In the optical recording/reproducing apparatus of the presentembodiment, the DVD-format code data is recorded onto a DVD-rewritabledisk (or a phase-change recording medium) by focusing a laser beamemitted by a laser diode, on the recording layer of the disk. Therecorded data is reproduced from the disk by the opticalrecording/reproducing apparatus. The optical recording/reproducingapparatus of the present embodiment employs the eight-to-sixteenmodulation (ESM) scheme as the data modulation method in order to carryout the pulse-width modulation (PWM) recording process for theDVD-rewritable disk.

[0331] In the optical recording/reproducing apparatus of FIG. 30, themulti-pulse drive current in which data is modulated is supplied to thelaser light source, and the laser light source emits the laser beam tothe DVD-rewritable disk. A stream of data blocks, including marks andspaces, are recorded onto the recording layer of the disk by focusingthe laser beam on the recording layer of the disk.

[0332] Generally, when recording data onto the phase-change recordingmedia by using the multi-pulse laser driving, the opticalrecording/reproducing apparatus is required to maintain the accuratepower levels of the laser optical power, including the peak power (Pw)corresponding to the peak-level drive current, the bias power (Pb)corresponding to the bias-level drive current, and the erase power (Pe)or space power corresponding to the erase-level drive current orspace-level drive current.

[0333] A description will now be provided of the automatic power control(APC) process which is performed by the optical recording/ reproducingapparatus of the present embodiment.

[0334] As shown in FIG. 30, the optical recording/reproducing apparatusof the present embodiment generally comprises a central processing unit(CPU) 1, a laser diode (LD) 2, a photodetector (PD) 3, a laser diodedriver (LDD) 4, a current-voltage converter 5, a bias-level currentdriver (BCD) 57, an erase-level current driver (ECD) 58, and apeak-level current driver (PCD) 59. A digital-to-analog (D/A) converter60 is provided between the CPU 1 and the BCD 57.

[0335] In the optical recording/reproducing apparatus of FIG. 30, theCPU 1 sets a peak-level increment current 507 at the output of thepeak-level current driver (PCD) 59 by supplying a peak-level control(PLC) signal 505 to the PCD 59. The CPU 1 sets an erase-level incrementcurrent 506 at the output of the erase-level current driver (ECD) 58 bysupplying an erase-level control (ELC) signal 504 to the ECD 58. The CPU1 sets a bias-level drive current 508 at the output of the bias-levelcurrent driver (BCD) 57 by supplying a target power signal (TPS) 512 tothe BCD 57 via the D/A converter 60.

[0336] Specifically, each of the ECD 58 and the PCD 59 is configured byusing a digital-to-analog converter (DAC). The digital erase-levelcontrol signal from the CPU 1 is received at the ECD 58, and, inresponse to the control signal, the ECD 58 outputs the analogerase-level increment current 506 to the LDD 4. The digital peak-levelcontrol signal from the CPU 1 is received at the PCD 59, and, inresponse to the control signal, the PCD 59 outputs the analog peak-levelincrement current 507 to the LDD 4.

[0337] In the present embodiment, the ECD 58 is configured such that theECD 58 selectively outputs one of a plurality of erase-level incrementcurrent signals to the LDD 4 through the signal line 506 in response tocontrol signals output by the CPU 1. Specifically, the ECD 58 isconstructed as shown in FIG. 32 (which will be explained later), andoutputs the erase-level increment current 506 to the LDD 4.

[0338] The LDD 4 receives the bias-level drive current 508, theerase-level increment current 506 and the peak-level increment current507, and determines the bias power Pb, the erase power Pe and the peakpower Pw for the laser diode 2 from the received drive currents. Inresponse to the control signals from the CPU 1, the LDD 4 supplies aselected one of the drive currents to the laser diode 2 at a controlledtime.

[0339] In the optical recording/reproducing apparatus, the CPU 1converts a sequence of input recording data blocks into aneight-to-sixteen modulation (ESM) signal as in the waveform indicated by(b) in FIG. 33. The CPU 1 further generates a multi-pulse laser drivingwaveform as in the laser drive waveform indicated by (c) in FIG. 33. Inaccordance with the multi-pulse laser driving waveform, the CPU 1supplies an erase-power enable (EPE) signal 501 and a peak-power enable(PPE) signal 502 to the LDD 4 as indicated by (b) and (c) in FIG. 34.

[0340] When the erase-power enable (EPE) signal 501 is set in the highlevel (H), the LDD 4 supplies a sum of the bias-level drive current 508and the erase-level increment current 506 to the LD 2. The LD 2 isdriven by such erase-level drive current to output the laser beam at theerase power (Pe). When the peak-power enable (PPE) signal 502 is set inthe high level (H), the LDD 4 supplies a sum of the bias-level drivecurrent 508 and the peak-level increment current 507 to the LD 2. The LD2 is driven by such peak-level drive current to output the laser beam atthe erase power (Pw).

[0341] When the drive current is supplied from the LDD4 to the LD 2, theLD 2 outputs the laser beam onto the phase-change recording medium, sothat the data is recorded onto or reproduced from the recording layer ofthe phase-change recording medium. The laser beam output by the LD 2 isreceived at the monitor photodetector (PD) 3. The monitor PD 3 outputs amonitor current that is proportional to the laser optical power of thereceived laser beam. The monitor current is supplied from the PD 3 tothe current-voltage converter 5 via a signal line 509. Thecurrent-voltage converter 5 outputs a power-monitor signal (PMS) 510based on the monitor current 509 supplied by the PD 3. The power monitorsignal 510 is supplied from the current-voltage converter 5 tosample-hold circuits 727 and 728 of the BCD 57. By utilizing thepower-monitor signal (PMS) 510 supplied by the current-voltage converter5, the BCD 57 performs the automatic power control (APC) process in theoptical recording/reproducing apparatus of the present embodiment.

[0342] As shown in FIG. 31, in the bias-level current driver (BCD) 57 ofthe present embodiment, two amplifiers 723 and 724 are provided, and thepower-monitor signal (PMS) 510, output by the current-voltage converter5, is supplied to each of the amplifiers 723 and 724. The sample/holdcircuit 727 is connected to the output of the amplifier 723 via ananalog switch 725, and the sample/hold circuit 728 is connected to theoutput of the amplifier 724 via an analog switch 726.

[0343] In the BCD 57 of FIG. 31, the amplifier 723, the switch 725 andthe sample/hold circuit 727 form part of an APC output feedback loopcircuit (indicated by the arrow A in FIG. 30) that is used when a normalrecording process is performed. The APC output feedback loop circuit iscomprised of the elements 723, 725 and 727, an inverting amplifier 731,a current control amplifier 732, the LDD 4, the LD 2, the monitor PD 3and the current-voltage converter 5. The target power signal 512, outputby the CPU 1 through the D/A converter 60, is supplied to the invertinginput of the amplifier 731, and the reference voltage Vref is suppliedto the non-inverting input of the amplifier 731. A sum of the outputsignal of the sample/hold circuit 727 and the output signal of theamplifier 731 is supplied to the inverting input of the amplifier 732,and the reference voltage Vref is supplied to the non-inverting input ofthe amplifier 732. The current-control amplifier 732 in the presentembodiment is configured by using an integrator circuit. The outputsignal of the amplifier 732 is supplied as the bias-level drive current508 to the LDD 4. In this manner, the APC output feedback loop is formedas indicated by the arrow A in FIG. 30.

[0344] In the BCD 57 of FIG. 31, the amplifier 724, the analog switch726 and the sample/hold circuit 728 form a special power setting circuitthat is used when a special power setting is performed to calculate alaser diode derivative efficiency (which will be explained later). Theoutput signal of the sample/hold circuit 728 is converted at ananalog-to-digital (A/D) converter 733 into a digital signal, and thisdigital signal is supplied from the BCD 57 to the CPU 1 as the digitalerase-power signal 515.

[0345] In the BCD 57 of FIG. 31, the erase-level select (ELS) signal514, output by the CPU 1, is supplied to each of two AND circuits 734and 735, and the erase-power sample (EPS) signal 513, output by the CPU1, is supplied to each of the AND circuits 734 and 735. The outputsignals of the AND circuits 734 and 735 control the open/close settingof the analog switches 725 and 726.

[0346] When a normal recording process is performed, the ELS signal 514,output by the CPU 1 to the BCD 57, is set to the low level (L). If theEPS signal 513 is set to the high level (H), the output signal of theAND circuit 734 sets the switch 725 to the high-level (H) condition sothat the switch 725 is turned ON. If the EPS signal 513 is set to thelow level (L), the output signal of the AND circuit 734 sets the switch725 to the low-level (L) condition so that the switch 725 is turned OFF.The switch 726 is always set to the low-level (L) condition so that theswitch 726 is turned OFF, regardless of whether the EPS signal 513 isset to the high level (H) or the low level (L). In this condition, thepower monitor signal (PMS) 510 is sampled and held by the sample/holdcircuit 727.

[0347] On the other hand, when the special power setting process isperformed, the ELS signal 514, output by the CPU 1 to the BCD 57, is setto the high level (H). Regardless of whether the EPS signal 513 is setto the high level (H) or the low level (L), the output signal of the ANDcircuit 734 always sets the switch 725 to the low-level (L) condition sothat the switch 725 is turned OFF. If the EPS signal 513 is set to thehigh level (H), the output signal of the AND circuit 735 sets the switch726 to the high-level (H) condition so that the switch 726 is turned ON.If the EPS signal 513 is set to the low level (L), the output signal ofthe AND circuit 735 sets the switch 726 to the low-level (H) conditionso that the switch 726 is turned OFF. In this condition, the powermonitor signal (PMS) 510 is sampled and held by the sample/hold circuit728.

[0348] As shown in FIG. 32, the erase-level current driver (ECD) 58 inthe present embodiment generally comprises a first digital-to-analogconverter (DAC) 836, a second digital-to-analog converter (DAC) 837, anda switch 838. The switch 838 has a high-level (H) condition and alow-level (L) condition. The erase-level select (ELS) signal 514, outputby the CPU 1, is supplied to the switch 838, and one of the high-level(H) condition and the low-level (L) condition is selected at the switch838 in accordance with the erase-level select (ELS) signal 514 suppliedby the CPU 1.

[0349] The first DAC 836 has an input connected to the CPU 1 via thesignal line 504, and has an output connected to the switch 838. When thelow-level (L) condition of the switch 838 is selected according to theELS signal 514 (or during the normal recording process), the ECD 58supplies an output signal of the first DAC 836 to the LDD 4 as theerase-level increment current 506. The second DAC 837 has an inputconnected to the CPU 1 via the signal line 504 a, and has an outputconnected to the switch 838. When the high-level (H) condition of theswitch 838 is selected according to the ELS signal 514 (or during thespecial power setting process), the ECD 58 supplies an output signal ofthe second DAC 837 to the LDD 4 as the erase-level increment current506.

[0350] A normal erase-level control (ELC) signal 504, which is output bythe CPU 1 when producing the normal erase power (Pe) of the laseroptical output, is received at the first DAC 836, and, in response tothe normal ELC signal 504, the DAC 836 outputs the normal erase-levelincrement current (EIC) to the switch 838. Usually when the erase power(Pe) of the laser optical output is produced, the low-level (L)condition of the switch 838 is selected according to the ELS signal 514.

[0351] A second erase-level control (ELC) signal 504 a, which is outputby the CPU 1 during the special power setting process, is received atthe second DAC 837, and, in response to the second ELC signal 504 a, theDAC 837 outputs a second erase-level increment current (EIC) to theswitch 838.

[0352] In the present embodiment, the frequency at which the executionof the special power setting process is initiated by the CPU 1 issmaller than the frequency at which the execution of the normal APCprocess is initiated by the CPU 1. An optimal value of the frequency ofexecution of the special power setting process may be experimentallydetermined depending on time-dependent variations of the derivativeefficiency of the LD 2.

[0353] A description will now be provided of the normal APC process thatis performed by the optical recording/reproducing apparatus of thepresent embodiment with reference to FIG. 35 and FIG. 36.

[0354]FIG. 35 shows a laser diode derivative efficiency used by theoptical recording/reproducing apparatus of FIG. 30.

[0355] The derivative efficiency “η” of the LD 2 used by the opticalrecording/reproducing apparatus of the present embodiment, is defined asbeing a gradient ΔP/ΔI of the optical power vs. drive currentcharacteristic curve shown in FIG. 35.

[0356] Suppose that the bias-level drive current corresponding to thebias power Pb, the erase-level drive current corresponding to the erasepower Pe, and the peak-level drive current corresponding to the peakpower Pw are represented by “Ib”, “Ie”, and “Iw”, respectively. As isapparent from the optical power vs. drive current characteristic curveof FIG. 35, the erase-level increment current “ΔIe” and the peak-levelincrement current “ΔIe+ΔIw” are represented by the following equations.

ΔIe=(Pe—Pb)/η

ΔIe+ΔIw=(Pe—Pb)/η

[0357] The erase-level increment current “ΔIe” and the peak-levelincrement current “ΔIe+ΔIw” can be calculated in accordance with theabove equations. In this case, the derivative efficiency “κ” of the LD 2is predetermined, and the calculations of the erase-level incrementcurrent “ΔIe” and the peak-level increment current “ΔIe+ΔIw” areperformed by using the predetermined derivative efficiency. As describedabove, the CPU 1 calculates the erase-level drive current “Ie” and thepeak-level drive current “Iw” based on the corrected erase-level drivecurrent and the derivative efficiency.

[0358]FIG. 36 shows the optical power vs. drive current characteristicsof the laser diode in the optical recording/reproducing apparatus ofFIG. 30.

[0359] As indicated in FIG. 36, the optical power vs. drive currentcharacteristic curve tends to shift and bend to the right withincreasing temperature, and the derivative efficiency of the laser diode(LD) 2 tends to vary with increasing temperature. If the derivativeefficiency varies, the errors of the calculated bias-level drive current“Ib” and the calculated peak-level drive current “Iw” will not benegligible.

[0360] As previously described, the conventional apparatus (disclosed inJapanese Laid-Open Patent Application No.9-171631) carries out the powercontrol process in which the bottom-level drive current to the laserdiode is corrected by using the detected peak power and the detectederase power, in order to take measures against a variation of thederivative efficiency. However, according to the above power controlprocess of the conventional apparatus, a problem arises in that theformation of a mark on the recording layer of the disk when the laserdiode is driven at the peak-level drive current in the non-pulsecondition becomes deficient.

[0361] In order to eliminate the above problem of the conventionalapparatus, the optical recording/reproducing apparatus of the presentembodiment is configured so that the erase-level current driver (ECD) 58selectively outputs one of the plurality of erase-level incrementcurrents to the LDD 4 in response to the control signals supplied by theCPU 1. The respective power levels of the laser optical power when theindividual erase-level increment currents are supplied to the LDD 4 aresampled and held by the sample/hold circuits of the BCD 57, and thecorresponding erase power sample (EPS) signals 515 are received at theCPU 1. Then, the CPU 1 calculates a derivative efficiency of the LD 2based on the erase power samples (EPS).

[0362] A description will now be provided of the special power settingprocess that is performed by the optical recording/ reproducingapparatus of the present embodiment with reference to FIG. 37 throughFIG. 39.

[0363]FIG. 37 is a time chart for explaining exemplary waveforms of theoutput signals of the elements of the optical recording/ reproducingapparatus of FIG. 30. FIG. 38 shows an example of detection oferase-level optical power at two sampling points used by the opticalrecording/ reproducing apparatus of FIG. 30. FIG. 39 shows a calculationof a laser diode derivative efficiency that is performed by the opticalrecording/reproducing apparatus of FIG. 30.

[0364] At a start of the special power setting process, the CPU 1outputs the second ELC signal 504 a to the second DAC 837, and thesecond DAC 837 outputs a second EIC to the switch 838. The high level(H) condition of the switch 838 is selected according to the ELS signal514, and the second EIC, supplied by the ECD 58, results in a firsterase power “Pe+α” of the laser beam of the LD 2. See the state (2)indicated in FIG. 37 and the detection of erase-level optical powershown in FIG. 38.

[0365] In the above-described condition, when recording a lOT space data“10TS” onto the disk, the CPU 1 sets the ELS signal 514 in the low level(L), and the DAC 837 supplies the second EIC to the LDD 4 as the EICsignal 506. Hence, only during the 10T period, the first erase power“Pe+α” of the laser beam of the LD 2 is produced.

[0366] In the above-described condition, a corresponding first erasepower sample (EPS) signal 114, output by the ADC 7, is received by theCPU 1. The CPU 1 stores the received EPS signal in a portion of thememory that is different from a memory portion in which the EPS signalobtained during the APC process is stored.

[0367] Immediately after the lOT space data is recorded onto the disk,the CPU 1 sets the ELS signal 514 to the low level (L). The low-level(L) condition of the switch 838 is selected according to the ELS signal514 so as to produce the normal erase power “Pe” of the laser beam ofthe LD 2. See the state (3) indicated in FIG. 37 and the detection oferase-level optical power shown in FIG. 38.

[0368] In the present embodiment, the state (2) and the state (3) arerepeated 8 times, and an average of the first erase power values “Pe +α”obtained through the repeated processed is calculated for the purpose ofincreasing the accuracy of the derivative efficiency calculation.

[0369] Usually, the peak power and the erase power of the laser diodeare set to the optimal values when performing a laser power calibrationon the phase-change recording disk, so as to retain good jittercharacteristics when reproducing the data from the disk. If an erasepower of the laser beam of the LD 2, different from the normal erasepower Pe, is produced for a too long time, the jitter characteristicswill deteriorate. In the present embodiment, immediately after the lOTspace data is formed on the disk with the first erase power, the switch838 is returned to the low-level (L) condition so as to produce thenormal erase power. Hence, the deterioration of the jittercharacteristics will be negligible.

[0370] Following the above repeated processes of the state (2) and thestate (3), the CPU 1 sends another second ELC signal 504 a to the secondDAC 837, and the second DAC 837 outputs another second EIC to the switch838. The high-level (H) condition of the switch 838 is selectedaccording to the ELS signal 514, and the second EIC, supplied by the ECD58, results in a second erase power “Pe—α” of the laser beam of the LD2. See the state (5) indicated in FIG. 37 and the detection oferase-level optical power shown in FIG. 38.

[0371] In the above-described condition, when recording a lOT space data“10TS” onto the disk, the CPU 1 sets the ELS signal 514 in the low state(L), and the DAC 837 supplies the second EIC to the LDD 4 via the switch838 as the erase-level increment current 506. Hence, only during the 10Tperiod, the second erase power “Pe—α” of the laser beam of the LD 2 isproduced.

[0372] In the above-described condition, a corresponding second erasepower sample (EPS) signal 515, output by the A/D converter 733 of theBCD 57, is received at the CPU 1. The CPU 1 stores the received secondEPS signal in the memory that is different from the EPS signal obtainedduring the APC process is stored.

[0373] Immediately after the 10T space data is recorded onto the disk,the CPU 1 sets the ELS signal 514 to the low level (L). The low-level(L) condition of the switch 838 is selected according to the ELS signal514 so as to produce the normal erase power “Pe” of the laser beam ofthe LD 2. See the state (6) indicated in FIG. 37 and the detection oferase-level optical power shown in FIG. 38.

[0374] In the present embodiment, the state (5) and the state (6) arerepeated 8 times, and an average of the second erase power values “Pe—α”obtained through the repeated processed is calculated for the purpose ofincreasing the accuracy of the derivative efficiency calculation.

[0375] The CPU 1 calculates a derivative efficiency “η” of the LD 2based on the first and second erase-power sample (EPS) signals (Pe +α,Pe—α) and the corresponding erase-level drive currents (Ie″, Ie′), inaccordance with the following equation. $\begin{matrix}{\eta = {\left\{ {\left( {{Pe} + \alpha} \right) - \left( {{Pe} - \alpha} \right)} \right\}/\left( {I_{e}^{\prime\prime} - I_{e}^{\prime}} \right)}} \\{= {2{\alpha/\left( {I_{e}^{\prime\prime} - I_{e}^{\prime}} \right)}}}\end{matrix}$

[0376] See the optical power vs. drive current characteristics shown inFIG. 39 for an example of the calculation of the derivative efficiencyused by the present embodiment.

[0377] If the setting of the second DAC 837 for the second erase-poweroutput can be performed timely, the first erase-power “Pe+α” laserdriving and the second erase-power “Pe—α” laser driving may be performedwithin a period the 10T space data is output. Alternatively, anintermediate period of the 10T space data output at the normal erasepower level may be interposed between the period of the firsterase-power “Pe+α” laser driving and the period of the seconderase-power “Pe—α” laser driving. In either case, in order to calculatean accurate derivative efficiency, the first and second erase-powerlaser driving must be performed within a comparatively short period.

[0378] The reason why the first erase-power “Pe+α” and the seconderase-power “Pe—α” are sampled for the calculation of the derivativeefficiency is to make use of a proper erase-level range of the laserdriving permitted for erasing data from the phase-change recordingmedium.

[0379] Usually, the erase power of the laser diode with respect to thephase-change recording disk is set to the optimal value when performinga laser power calibration process on the disk. The optimal value of theerase power, which is set by the laser power calibration process,normally lies around at the middle point of the proper erase-level rangeof the disk.

[0380] In order to obtain an accurate derivative efficiency of the laserdiode with a smaller calculation error, it is desirable to make thedifference between the erase-power levels at the two sampling points aslarge as possible. In the above-described embodiment, the firsterase-power “Pe+α” and the second erase-power “Pe—α”, which fall withinthe proper erase-level range, are sampled and the derivative efficiencyis calculated accordingly. The optical recording/reproducing apparatusof the present embodiment can provide accurate calculation of thederivative efficiency with little calculation errors and prevent thedeterioration of the overwriting characteristics and the deficiency ofthe erasing.

[0381] Further, in the present embodiment, the CPU 1 calculates the biaspower “Pb” and the peak power “Pw” based on the calculated derivativeefficiency in a manner similar to the above APC process shown in FIG.35. Accordingly, the optical recording/reproducing apparatus of thepresent embodiment is effective in maintaining the accurate recordingpower levels of the laser optical power, including the peak power Pw,the erase power Pe and the bias power Pb even when the light receivingmodule with the limited bandwidth is used. The opticalrecording/reproducing apparatus is effective in preventing the deficientformation of a mark on the disk when recording data onto the disk.

[0382] Further, the optical recording/reproducing apparatus of thepresent embodiment is configured so that the erase-level current driver(ECD) 58 selectively outputs one of the plurality of erase-levelincrement currents to the LDD 4 through the signal line 506 in responseto the control signals supplied by the CPU 1. The respective powerlevels of the laser optical power when the individual erase-levelincrement currents are supplied to the LDD 4 are sampled and held by thesample/hold circuit, and the corresponding erase power sample (EPS)signals are received by the CPU 1. Then, the CPU 1 calculates aderivative efficiency of the LD 2 based on the erase power samples (EPS)at the plural sampling points. Therefore, the opticalrecording/reproducing apparatus of the present embodiment is effectivein maintaining the accurate recording power levels of the laser opticalpower even when the light-receiving module with the limited bandwidth isused. The optical recording/reproducing apparatus is effective inpreventing the deficient formation of a mark on the disk when recordingdata onto the disk.

[0383] Further, the optical recording/reproducing apparatus of thepresent embodiment is configured so that one of the plurality oferase-level increment currents, supplied from the ECD 58 to the LDD 4,is changed to another during a period a long space data having a datalength longer than a predetermined time is formed on the medium, and theerase-level increment current is returned to the original erase-levelincrement current immediately after an end of the period. Therefore, thedeterioration of the jitter characteristics will be negligible.

[0384] Further, the optical recording/reproducing apparatus of thepresent embodiment is configured so that the first erase-power “Pe +α”and the second erase-power “Pe—α”, which are obtained by increasing ordecreasing the normal erase power “Pe” by the value of α, are sampledfor the calculation of the derivative efficiency. Therefore, it ispossible to positively utilize the proper erase-level range of the laserdriving permitted for erasing data from the recording medium.

[0385] Further, the optical recording/reproducing apparatus of thepresent embodiment is configured such that the first erase-power “Pe+α”and the second erase-power “Pe—α”, which are obtained by increasing ordecreasing the normal erase power “Pe” by the value of α, are includedin the proper erase-level range for the recording medium. The opticalrecording/reproducing apparatus of the present embodiment is effectivein preventing the deterioration of the overwriting characteristics andthe deficiency of the erasing.

[0386] In the above-described embodiment, a single sample/hold circuit727 and a single sample/hold circuit 728 are provided in the bias-levelcurrent driver 57. Alternatively, plural sample/hold circuits 727 andplural sample/hold circuits 728 may be provided in the bias-levelcurrent driver 57.

[0387] The present invention is not limited to the above-describedembodiments and variations, and modifications may be made withoutdeparting from the scope of the present invention.

[0388] Further, the present invention is based on Japanese priorityapplication No. 11-208723, filed on Jul. 23, 1999, Japanese priorityapplication No. 11-227922, filed on Aug. 11, 1999, Japanese priorityapplication No. 2000-139531, filed on May 12, 2000, and Japanesepriority application No. 2000-222428, filed on Jul. 24, 2000, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. An optical recording/reproducing apparatus forrecording a sequence of data blocks onto an optical recording medium byusing a laser driving current waveform to control emission of a laserbeam by a semiconductor laser, and for reproducing the data blocks fromthe medium, the waveform including a sequence of mark and space dataportions each having a data length that corresponds to a multiple of aperiod of a channel clock based on a recording data modulation method,the optical recording/reproducing apparatus comprising: a semiconductorlaser driver supplying a selected one of a plurality of drive currents,including at least a first-level drive current and a second-level drivecurrent, to the semiconductor laser to control the emission of a laserbeam by the laser; a current driver selectively outputting one of aplurality of increment currents to the laser driver in response tocontrol signals, the plurality of increment currents including a firstincrement current supplied to the laser driver during an automatic powercontrol process and a second increment current supplied to the laserdriver during a special power setting process; a detection unitdetecting a first power sample signal, at a first sampling point of thewaveform, from the laser beam emitted when the first increment currentis supplied to the laser driver, and the detection unit detecting asecond power sample signal, at a second sampling point of the waveform,from the laser beam emitted when the second increment current issupplied to the laser driver; and a calculation unit calculating aderivative efficiency of the laser based on the first and second powersample signals detected by the detection unit, so that the drivecurrents of the laser driver, supplied to the laser, are controlledbased on the calculated derivative efficiency.
 2. The opticalrecording/reproducing apparatus according to claim 1, wherein thecurrent driver is configured into an erase-level current driver whichselectively outputs one of a plurality of erase-level increment currentsto the laser driver in response to erase-level control signals, theplurality of erase-level increment currents including a firsterase-level increment current supplied to the laser driver during theautomatic power control process and a second erase-level incrementcurrent supplied to the laser driver during the special power settingprocess.
 3. The optical recording/reproducing apparatus according toclaim 2, wherein the erase-level current driver comprises: a switchhaving a first state and a second state, one of which is selected at theswitch in response to an erase-level select signal; a first currentsource, connected to the switch, which supplies the first erase-levelincrement current to the laser driver via the switch when the firststate is selected; and a second current source, connected to the switch,which supplies the second erase-level increment current to the laserdriver via the switch when the second state is selected.
 4. The opticalrecording/reproducing apparatus according to claim 2, wherein theerase-level current driver is configured so that the first erase-levelincrement current, supplied from the erase-level current driver to thelaser driver, is changed to the second erase- level increment currentduring a period a space data having a data length larger than apredetermined time is formed on the medium.
 5. The opticalrecording/reproducing apparatus according to claim 2, wherein theerase-level current driver is configured so that the first and seconderase-level increment currents supplied to the laser driver result infirst and second erase powers of the laser optical output that areobtained by increasing or decreasing a normal erase power of the laseroptical output by a predetermined value.
 6. The opticalrecording/reproducing apparatus according to claim 5, wherein theerase-level current driver is configured so that the first and seconderase powers of the laser optical output, which are obtained byincreasing or decreasing the normal erase power of the laser opticaloutput by the predetermined value, are included in a proper erase-levelrage for the medium.
 7. The optical recording/reproducing apparatusaccording to claim 2, wherein the calculation unit is configured sothat, when a difference between a normal erase power sample obtained bythe first erase-level increment current and an upper limit of a propererase-level range for the medium is less than a reference value, thecalculation unit calculates a derivative efficiency of the laser basedon the normal erase power sample and an erase power sample that isobtained by decreasing the normal erase power sample by a predeterminedvalue, and when the difference between the normal erase power sample anda lower limit of the proper erase-level range is less than the referencevalue, the calculation unit calculates a derivative efficiency of thelaser based on the normal erase power sample and an erase-power samplethat is obtained by increasing the normal erase power sample by thepredetermined value.
 8. The optical recording/reproducing apparatusaccording to claim 1, wherein the current driver is configured into aspace-level current driver that selectively outputs one of a pluralityof space-level increment currents to the laser driver in response tospace-level control signals, the plurality of space-level incrementcurrents including a first space-level increment current supplied to thelaser driver during the automatic power control process and a secondspace-level increment current supplied to the laser driver during thespecial power setting process, the second space-level increment currentsupplied to the laser driver resulting in a drive current produced bythe laser driver, which is equal to a peak-level drive current to thelaser.
 9. The optical recording/reproducing apparatus according to claim8, further comprising a bias current source supplying a bias current tothe laser driver, wherein the laser driver receives the bias current,supplied by the bias current source, and the selected one of theplurality of space-level increment currents, supplied by the space-levelcurrent driver, and the laser driver supplying a sum of the receivedbias current and the received space-level increment current to the laseras a space-level drive current that results in a space power of thelaser optical output.
 10. The optical recording/reproducing apparatusaccording to claim 8, wherein the space-level current driver comprises:a switch having a first state and a second state, one of which isselected at the switch in response to a space-level select signal; afirst current source, connected to the switch, which supplies the firstspace-level increment current to the laser driver via the switch whenthe first state is selected; and a second current source, connected tothe switch, which supplies the second space-level increment current tothe laser driver via the switch when the second state is selected. 11.The optical recording/reproducing apparatus according to claim 8,wherein the space-level current driver is configured so that the firstspace-level increment current, supplied from the space-level currentdriver to the laser driver, is changed to the second space-levelincrement current during a period a mark data having a data lengthlarger than a predetermined time is formed on the medium.
 12. Theoptical recording/reproducing apparatus according to claim 1, whereinthe current driver is configured into a bottom-level current driver thatselectively outputs one of a plurality of bottom-level incrementcurrents to the laser driver in response to bottom-level controlsignals, the plurality of bottom-level increment currents including afirst bottom-level increment current supplied to the laser driver duringthe automatic power control process and a second bottom-level incrementcurrent supplied to the laser driver during the special power settingprocess, the second bottom-level increment current supplied to the laserdriver resulting in a drive current produced by the laser driver, whichis equal to a peak-level drive current to the laser.
 13. The opticalrecording/reproducing apparatus according to claim 12, furthercomprising a bias current source supplying a bias current to the laserdriver, wherein the laser driver receives the bias current, supplied bythe bias current source, and the selected one of the plurality ofbottom-level increment currents, supplied by the bottom-level currentdriver, and the laser driver supplying a sum of the received biascurrent and the received bottom-level increment current to the laser asa bottom-level drive current that results in a bottom power of the laseroptical output.
 14. The optical recording/reproducing apparatusaccording to claim 12, wherein the bottom-level current drivercomprises: a switch having a first state and a second state, one ofwhich is selected at the switch in response to a bottom-level selectsignal; a first current source, connected to the switch, which suppliesthe first bottom-level increment current to the laser driver via theswitch when the first state is selected; and a second current source,connected to the switch, which supplies the second bottom-levelincrement current to the laser driver via the switch when the secondstate is selected.
 15. The optical recording/reproducing apparatusaccording to claim 12, wherein the bottom-level current driver isconfigured so that the first bottom-level increment current, suppliedfrom the bottom-level current driver to the laser driver, is changed tothe second bottom-level increment current during a period a mark datahaving a data length larger than a predetermined time is formed on themedium.
 16. An optical recording/reproducing apparatus for recording asequence of data blocks onto an optical recording medium by using alaser driving current waveform to control emission of a laser beam by asemiconductor laser, and reproducing the data blocks from the medium,the waveform including a sequence of mark and space data portions eachhaving a data length that corresponds to a multiple of a period of achannel clock based on a recording data modulation method, the opticalrecording/reproducing apparatus comprising: a semiconductor laser driversupplying a selected one of a plurality of drive currents, including atleast a bias-level drive current and a peak-level drive current, to thesemiconductor laser to control the emission of a laser beam by thelaser; a bias-level current driver for selectively outputting one of aplurality of bias-level drive currents to the laser driver in responseto control signals, the plurality of bias-level drive currents includinga first drive current supplied to the laser driver during an automaticpower control APC process and a second drive current supplied to thelaser driver during an automatic current control ACC process; and acontrol unit selectively executing one of the APC process and the ACCprocess on the current driver by supplying the control signals to thecurrent driver, the control unit outputting a sampling signal to thecurrent driver in response to a power-monitor signal of the laser beamemitted by the laser when recording data onto the recording medium,wherein, when the control unit outputs the sampling signal within apredetermined time, the control unit continuously executes the APCprocess on the current driver so that the current driver supplies thefirst drive current to the laser driver, and when the control unit doesnot output the sampling signal over a period exceeding the predeterminedtime, the control unit terminates the execution of the APC process andstarts the execution of the ACC process by using a switching unit thatoperates in response to the control signals supplied to the currentdriver, so that the current driver supplies the second drive current tothe laser driver.
 17. The optical recording/reproducing apparatusaccording to claim 16, wherein the semiconductor laser driver isconfigured to supply a selected one of the plurality of drive currents,including the bias-level drive current, the peak-level drive current andan erase-level drive current, to the semiconductor laser so as tocontrol the emission of a laser beam by the laser.
 18. The opticalrecording/reproducing apparatus according to claim 16, wherein thecontrol unit is configured such that, after the execution of the ACCprocess is started, the control unit immediately restarts the executionof the APC process.
 19. The optical recording/reproducing apparatusaccording to claim 16, further comprising: a peak-level current driveroutputting a peak-level increment current to the laser driver inresponse to a peak-level control signal supplied by the control unit;and an erase-level current driver outputting an erase-level incrementcurrent to the laser driver in response to an erase-level control signalsupplied by the control unit.
 20. The optical recording/reproducingapparatus according to claim 16, wherein the current driver includes amonostable multivibrator that receives the sampling signal output by thecontrol unit, and the multivibrator outputs a control signal to theswitching unit.
 21. The optical recording/reproducing apparatusaccording to claim 16, wherein the current driver includes a counterunit having a clock and a counter that receives the sampling signaloutput by the control unit, the clock outputting a clock signal at apredetermined frequency, and, when the number of the clock signalscounted by the counter exceeds a predetermined value, the counter unitoutputs a control signal to the switching unit.
 22. The opticalrecording/reproducing apparatus according to claim 16, furthercomprising a detection unit detecting a first power sample signal at afirst sampling point of the waveform from the laser beam emitted whenthe first increment current is supplied to the laser driver, and thedetection unit detecting a second power sample signal at a secondsampling point of the waveform from the laser beam emitted when thesecond increment current is supplied to the laser drive.
 23. The opticalrecording/reproducing apparatus according to claim 22, furthercomprising a calculation unit calculating a derivative efficiency of thelaser based on the first and second power sample signals detected by thedetection unit, so that the drive currents of the laser driver, suppliedto the laser, are controlled based on the calculated derivativeefficiency.
 24. The optical recording/reproducing apparatus according toclaim 16, wherein the control unit outputs the sampling signal to thecurrent driver when a data length of a space data to be recorded ontothe recording medium exceeds a predetermined time.
 25. The opticalrecording/reproducing apparatus according to claim 16, furthercomprising: an erase-level current driver selectively outputting one ofa plurality of erase-level increment currents to the laser driver inresponse to erase-level control signals, the plurality of erase-levelincrement currents including a first erase-level increment currentsupplied to the laser driver during the automatic power control processand a second erase-level increment current supplied to the laser driverduring a special power setting process; a detection unit detecting afirst power sample at a first sampling point of the waveform from thelaser beam emitted when the first increment current is supplied to thelaser driver, and the detection unit detecting a second power sample ata second sampling point of the waveform from the laser beam emitted whenthe second increment current is supplied to the laser driver; and acalculation unit calculating a derivative efficiency of the laser basedon the first and second power sample signals detected by the detectionunit, so that the drive currents of the laser driver, supplied to thelaser, are controlled based on the calculated derivative efficiency. 26.The optical recording/reproducing apparatus according to claim 25,wherein the erase-level current driver comprises: a switch having afirst state and a second state, one of which is selected at the switchin response to an erase-level select signal; a first digital-to-analogconverter, connected to the switch, which supplies the first erase-levelincrement current to the laser driver via the switch when the firststate is selected; and a second digital-to-analog converter, connectedto the switch, which supplies the second erase-level increment currentto the laser driver via the switch when the second state is selected.27. The optical recording/reproducing apparatus according to claim 25,wherein the erase-level current driver is configured so that the firsterase-level increment current, supplied from the erase-level currentdriver to the laser driver, is changed to the second erase-levelincrement current during a period a space data having a data lengthlarger than a predetermined time is formed on the medium.
 28. Theoptical recording/reproducing apparatus according to claim 25, whereinthe erase-level current driver is configured so that the first andsecond erase-level increment currents supplied to the laser driverresult in first and second erase powers of the laser optical output thatare obtained by increasing or decreasing a normal erase power of thelaser optical output by a predetermined value.
 29. The opticalrecording/reproducing apparatus according to claim 28, wherein theerase-level current driver is configured so that the first and seconderase powers of the laser optical output, which are obtained byincreasing or decreasing the normal erase power of the laser opticaloutput by the predetermined value, are included in a proper erase-levelrage for the medium.
 30. The optical recording/reproducing apparatusaccording to claim 25, wherein the calculation unit is configured sothat, when a difference between a normal erase power sample obtained bythe first erase-level increment current and an upper limit of a propererase-level range for the medium is less than a reference value, thecalculation unit calculates a derivative efficiency of the laser basedon the normal erase power sample and an erase power sample that isobtained by decreasing the normal erase power sample by a predeterminedvalue, and when the difference between the normal erase power sample anda lower limit of the proper erase-level range is less than the referencevalue, the calculation unit calculates a derivative efficiency of thelaser based on the normal erase power sample and an erase-power samplethat is obtained by increasing the normal erase power sample by thepredetermined value.